Update to 1.11.2

build.gradle

@@ -28,7 +28,7 @@
 archivesBaseName = "ComputerCraft"
 
 minecraft {
-    version = "1.9.4-12.17.0.1959"
+    version = "1.11.2-13.20.0.2294"
     runDir = "run"
     replace '${version}', project.version
 
@@ -37,7 +37,7 @@
     // stable_#            stables are built at the discretion of the MCP team.
     // Use non-default mappings at your own risk. they may not allways work.
     // simply re-run your setup task after changing the mappings to update your workspace.
-    mappings = "snapshot_20160518"
+    mappings = "snapshot_20161227"
     // makeObfSourceJar = false // an Srg named sources jar is made by default. uncomment this to disable.
 }
 

src/main/java/dan200/computercraft/ComputerCraft.java

@@ -58,6 +58,7 @@
 import net.minecraft.server.MinecraftServer;
 import net.minecraft.util.EnumFacing;
 import net.minecraft.util.EnumHand;
+import net.minecraft.util.NonNullList;
 import net.minecraft.util.SoundEvent;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.World;
@@ -75,6 +76,7 @@
 import org.apache.commons.io.IOUtils;
 import org.apache.logging.log4j.Logger;
 
+import javax.annotation.Nonnull;
 import java.io.*;
 import java.net.MalformedURLException;
 import java.net.URISyntaxException;
@@ -96,7 +98,7 @@
 )
 public class ComputerCraft
 {
-    public static final String MOD_ID = "ComputerCraft";
+    public static final String MOD_ID = "computercraft";
     public static final String LOWER_ID = "computercraft";
 
     // GUI IDs
@@ -462,7 +464,7 @@ public static void playRecord( SoundEvent record, String recordInfo, World world
         proxy.playRecord( record, recordInfo, world, pos );
     }
 
-    public static String getRecordInfo( ItemStack recordStack )
+    public static String getRecordInfo( @Nonnull ItemStack recordStack )
     {
         return proxy.getRecordInfo( recordStack );
     }
@@ -714,9 +716,9 @@ public static int getBundledRedstoneOutput( World world, BlockPos pos, EnumFacin
         return combinedSignal;
     }
 
-    public static IMedia getMedia( ItemStack stack )
+    public static IMedia getMedia( @Nonnull ItemStack stack )
     {
-        if( stack != null )
+        if( !stack.isEmpty() )
         {
             // Try the handlers in order:
             for( IMediaProvider mediaProvider : mediaProviders )
@@ -744,14 +746,14 @@ public static IPocketUpgrade getPocketUpgrade(String id) {
         return pocketUpgrades.get( id );
     }
 
-    public static IPocketUpgrade getPocketUpgrade( ItemStack stack )
+    public static IPocketUpgrade getPocketUpgrade( @Nonnull ItemStack stack )
     {
-        if( stack == null ) return null;
+        if( stack.isEmpty() ) return null;
 
         for (IPocketUpgrade upgrade : pocketUpgrades.values())
         {
             ItemStack craftingStack = upgrade.getCraftingItem();
-            if( craftingStack != null && InventoryUtil.areItemsStackable( stack, craftingStack ) )
+            if( !craftingStack.isEmpty() && InventoryUtil.areItemsStackable( stack, craftingStack ) )
             {
                 return upgrade;
             }
@@ -1010,12 +1012,12 @@ public static ITurtleUpgrade getTurtleUpgrade( int legacyID )
         return turtleProxy.getTurtleUpgrade( legacyID );
     }
 
-    public static ITurtleUpgrade getTurtleUpgrade( ItemStack item )
+    public static ITurtleUpgrade getTurtleUpgrade( @Nonnull ItemStack item )
     {
         return turtleProxy.getTurtleUpgrade( item );
     }
 
-    public static void addAllUpgradedTurtles( List<ItemStack> list )
+    public static void addAllUpgradedTurtles( NonNullList<ItemStack> list )
     {
         turtleProxy.addAllUpgradedTurtles( list );
     }

src/main/java/dan200/computercraft/api/pocket/IPocketUpgrade.java

@@ -48,9 +48,9 @@ public interface IPocketUpgrade
      * pocket computer which holds this upgrade. This item stack is also used to determine the upgrade given by
      * {@code pocket.equip()}/{@code pocket.unequip()}.
      *
-     * @return The item stack used for crafting. This can be {@code null} if crafting is disabled.
+     * @return The item stack used for crafting. This can be {@link ItemStack#EMPTY} if crafting is disabled.
      */
-    @Nullable
+    @Nonnull
     ItemStack getCraftingItem();
 
     /**

src/main/java/dan200/computercraft/api/turtle/ITurtleUpgrade.java

@@ -76,9 +76,9 @@ public interface ITurtleUpgrade
      * with to create a turtle which holds this upgrade. This item stack is also used
      * to determine the upgrade given by {@code turtle.equip()}
      *
-     * @return The item stack to craft with, or {@code null} if it cannot be crafted.
+     * @return The item stack to craft with, or {@link ItemStack#EMPTY} if it cannot be crafted.
      */
-    @Nullable
+    @Nonnull
     ItemStack getCraftingItem();
 
     /**

src/main/java/dan200/computercraft/client/gui/GuiConfigCC.java

@@ -41,6 +41,19 @@ public void initialize( Minecraft minecraft )
         }
 
         @Override
+        public boolean hasConfigGui()
+        {
+            return true;
+        }
+
+        @Override
+        public GuiScreen createConfigGui( GuiScreen parentScreen )
+        {
+            return new GuiConfigCC( parentScreen );
+        }
+
+        @Override
+        @Deprecated
         public Class<? extends GuiScreen> mainConfigGuiClass()
         {
             return GuiConfigCC.class;
@@ -53,6 +66,7 @@ public Set<RuntimeOptionCategoryElement> runtimeGuiCategories()
         }
 
         @Override
+        @Deprecated
         public RuntimeOptionGuiHandler getHandlerFor( RuntimeOptionCategoryElement runtimeOptionCategoryElement )
         {
             return null;

src/main/java/dan200/computercraft/client/gui/widgets/Widget.java

@@ -16,6 +16,8 @@
 import net.minecraft.item.ItemStack;
 import org.lwjgl.opengl.GL11;
 
+import javax.annotation.Nonnull;
+
 public abstract class Widget extends Gui
 {
     private WidgetContainer m_parent;
@@ -322,9 +324,9 @@ protected void drawTooltip( String[] lines, int x, int y )
         }
     }
 
-    protected void drawItemStack( int x, int y, ItemStack stack )
+    protected void drawItemStack( int x, int y, @Nonnull ItemStack stack )
     {
-        if( stack != null )
+        if( !stack.isEmpty() )
         {
             GlStateManager.color( 1.0f, 1.0f, 1.0f, 1.0f );
             GlStateManager.enableLighting();

src/main/java/dan200/computercraft/client/proxy/ComputerCraftProxyClient.java

@@ -301,7 +301,7 @@ public Object getFixedWidthFontRenderer()
     }
 
     @Override
-    public String getRecordInfo( ItemStack recordStack )
+    public String getRecordInfo( @Nonnull ItemStack recordStack )
     {
         List<String> info = new ArrayList<String>( 1 );
         recordStack.getItem().addInformation( recordStack, null, info, false );
@@ -351,7 +351,7 @@ public Object getTurtleGUI( InventoryPlayer inventory, TileTurtle turtle )
     public Object getPrintoutGUI( EntityPlayer player, EnumHand hand )
     {
         ContainerHeldItem container = new ContainerHeldItem( player, hand );
-        if( container.getStack() != null && container.getStack().getItem() instanceof ItemPrintout )
+        if( container.getStack().getItem() instanceof ItemPrintout )
         {
             return new GuiPrintout( container );
         }
@@ -362,7 +362,7 @@ public Object getPrintoutGUI( EntityPlayer player, EnumHand hand )
     public Object getPocketComputerGUI( EntityPlayer player, EnumHand hand )
     {
         ContainerPocketComputer container = new ContainerPocketComputer( player, hand );
-        if( container.getStack() != null && container.getStack().getItem() instanceof ItemPocketComputer )
+        if( container.getStack().getItem() instanceof ItemPocketComputer )
         {
             return new GuiPocketComputer( container );
         }

src/main/java/dan200/computercraft/client/render/TurtleSmartItemModel.java

@@ -103,7 +103,7 @@ public TurtleSmartItemModel()
         {
             @Nonnull
             @Override
-            public IBakedModel handleItemState( @Nonnull IBakedModel originalModel, ItemStack stack, @Nullable World world, @Nullable EntityLivingBase entity)
+            public IBakedModel handleItemState( @Nonnull IBakedModel originalModel, @Nonnull ItemStack stack, @Nullable World world, @Nullable EntityLivingBase entity)
             {
                 ItemTurtleBase turtle = (ItemTurtleBase) stack.getItem();
                 ComputerFamily family = turtle.getFamily( stack );

src/main/java/dan200/computercraft/shared/common/BlockGeneric.java

@@ -62,7 +62,8 @@ public final List<ItemStack> getDrops( IBlockAccess world, BlockPos pos, @Nonnul
 
     @Nonnull
     @Override
-    public final IBlockState onBlockPlaced( World world, BlockPos pos, EnumFacing side, float hitX, float hitY, float hitZ, int damage, EntityLivingBase placer )
+    @Deprecated
+    public final IBlockState getStateForPlacement( World world, BlockPos pos, EnumFacing side, float hitX, float hitY, float hitZ, int damage, EntityLivingBase placer )
     {
         return getDefaultBlockState( damage, side );
     }
@@ -102,7 +103,7 @@ public final void dropAllItems( World world, BlockPos pos, boolean creative )
         }
     }
 
-    public final void dropItem( World world, BlockPos pos, ItemStack stack )
+    public final void dropItem( World world, BlockPos pos, @Nonnull ItemStack stack )
     {
         Block.spawnAsEntity( world, pos, stack );
     }
@@ -130,17 +131,11 @@ public final ItemStack getPickBlock( @Nonnull IBlockState state, RayTraceResult
             TileGeneric generic = (TileGeneric)tile;
             return generic.getPickedItem();
         }
-        return null;
+        return ItemStack.EMPTY;
     }
 
     @Override
-    public final ItemStack createStackedBlock( @Nonnull IBlockState state )
-    {
-        return null;
-    }
-
-    @Override
-    public final boolean onBlockActivated( World world, BlockPos pos, IBlockState state, EntityPlayer player, EnumHand hand, ItemStack stack, EnumFacing side, float hitX, float hitY, float hitZ )
+    public final boolean onBlockActivated( World world, BlockPos pos, IBlockState state, EntityPlayer player, EnumHand hand, EnumFacing side, float hitX, float hitY, float hitZ )
     {
         TileEntity tile = world.getTileEntity( pos );
         if( tile != null && tile instanceof TileGeneric )
@@ -153,7 +148,7 @@ public final boolean onBlockActivated( World world, BlockPos pos, IBlockState st
 
     @Override
     @Deprecated
-    public final void neighborChanged( IBlockState state, World world, BlockPos pos, Block block )
+    public final void neighborChanged( IBlockState state, World world, BlockPos pos, Block block, BlockPos neighorPos )
     {
         TileEntity tile = world.getTileEntity( pos );
         if( tile != null && tile instanceof TileGeneric )
@@ -187,7 +182,7 @@ public final boolean isSideSolid( IBlockState state, @Nonnull IBlockAccess world
     }
 
     @Override
-    public final boolean canBeReplacedByLeaves( IBlockState state, IBlockAccess world, BlockPos pos )
+    public final boolean canBeReplacedByLeaves( @Nonnull IBlockState state, @Nonnull IBlockAccess world, @Nonnull BlockPos pos )
     {
         return false; // Generify me if anyone ever feels the need to change this
     }
@@ -196,7 +191,7 @@ public final boolean canBeReplacedByLeaves( IBlockState state, IBlockAccess worl
     public float getExplosionResistance( World world, BlockPos pos, @Nonnull Entity exploder, Explosion explosion )
     {
         TileEntity tile = world.getTileEntity( pos );
-        if( tile != null && tile instanceof TileGeneric && tile.hasWorldObj() )
+        if( tile != null && tile instanceof TileGeneric && tile.hasWorld() )
         {
             TileGeneric generic = (TileGeneric)tile;
             if( generic.isImmuneToExplosion( exploder ) )
@@ -213,7 +208,7 @@ public float getExplosionResistance( World world, BlockPos pos, @Nonnull Entity
     public final AxisAlignedBB getBoundingBox( IBlockState state, IBlockAccess world, BlockPos pos )
     {
         TileEntity tile = world.getTileEntity( pos );
-        if( tile != null && tile instanceof TileGeneric && tile.hasWorldObj() )
+        if( tile != null && tile instanceof TileGeneric && tile.hasWorld() )
         {
             TileGeneric generic = (TileGeneric)tile;
             return generic.getBounds();
@@ -231,10 +226,10 @@ public final AxisAlignedBB getSelectedBoundingBox( IBlockState state, @Nonnull W
 
     @Override
     @Deprecated
-    public final AxisAlignedBB getCollisionBoundingBox( IBlockState state, @Nonnull World world, @Nonnull BlockPos pos )
+    public final AxisAlignedBB getCollisionBoundingBox( IBlockState state, @Nonnull IBlockAccess world, @Nonnull BlockPos pos )
     {
         TileEntity tile = world.getTileEntity( pos );
-        if( tile != null && tile instanceof TileGeneric && tile.hasWorldObj() )
+        if( tile != null && tile instanceof TileGeneric && tile.hasWorld() )
         {
             TileGeneric generic = (TileGeneric)tile;
 
@@ -259,10 +254,10 @@ public final AxisAlignedBB getCollisionBoundingBox( IBlockState state, @Nonnull
 
     @Override
     @Deprecated
-    public final void addCollisionBoxToList( IBlockState state, @Nonnull World world, @Nonnull BlockPos pos, @Nonnull AxisAlignedBB bigBox, @Nonnull List<AxisAlignedBB> list, Entity entity )
+    public final void addCollisionBoxToList( IBlockState state, @Nonnull World world, @Nonnull BlockPos pos, @Nonnull AxisAlignedBB bigBox, @Nonnull List<AxisAlignedBB> list, Entity entity, boolean p_185477_7_ )
     {
         TileEntity tile = world.getTileEntity( pos );
-        if( tile != null && tile instanceof TileGeneric && tile.hasWorldObj() )
+        if( tile != null && tile instanceof TileGeneric && tile.hasWorld() )
         {
             TileGeneric generic = (TileGeneric)tile;
 
@@ -305,7 +300,7 @@ public final boolean canConnectRedstone( IBlockState state, IBlockAccess world,
     public final int getStrongPower( IBlockState state, IBlockAccess world, BlockPos pos, EnumFacing oppositeSide )
     {
         TileEntity tile = world.getTileEntity( pos );
-        if( tile != null && tile instanceof TileGeneric && tile.hasWorldObj() )
+        if( tile != null && tile instanceof TileGeneric && tile.hasWorld() )
         {
             TileGeneric generic = (TileGeneric)tile;
             return generic.getRedstoneOutput( oppositeSide.getOpposite() );
@@ -334,7 +329,7 @@ public boolean getBundledRedstoneConnectivity( World world, BlockPos pos, EnumFa
     public int getBundledRedstoneOutput( World world, BlockPos pos, EnumFacing side )
     {
         TileEntity tile = world.getTileEntity( pos );
-        if( tile != null && tile instanceof TileGeneric && tile.hasWorldObj() )
+        if( tile != null && tile instanceof TileGeneric && tile.hasWorld() )
         {
             TileGeneric generic = (TileGeneric)tile;
             return generic.getBundledRedstoneOutput( side );

src/main/java/dan200/computercraft/shared/common/ColourableRecipe.java

@@ -6,11 +6,11 @@
 import net.minecraft.inventory.InventoryCrafting;
 import net.minecraft.item.ItemStack;
 import net.minecraft.item.crafting.IRecipe;
+import net.minecraft.util.NonNullList;
 import net.minecraft.world.World;
 import net.minecraftforge.common.ForgeHooks;
 
 import javax.annotation.Nonnull;
-import javax.annotation.Nullable;
 
 public class ColourableRecipe implements IRecipe
 {
@@ -22,7 +22,7 @@ public boolean matches( @Nonnull InventoryCrafting inv, @Nonnull World worldIn )
         for( int i = 0; i < inv.getSizeInventory(); i++ )
         {
             ItemStack stack = inv.getStackInSlot( i );
-            if( stack == null ) continue;
+            if( stack.isEmpty() ) continue;
 
             if( stack.getItem() instanceof IColouredItem )
             {
@@ -42,11 +42,11 @@ else if( ColourUtils.getStackColour( stack ) >= 0 )
         return hasColourable && hasDye;
     }
 
-    @Nullable
+    @Nonnull
     @Override
     public ItemStack getCraftingResult( @Nonnull InventoryCrafting inv )
     {
-        ItemStack colourable = null;
+        ItemStack colourable = ItemStack.EMPTY;
 
         ColourTracker tracker = new ColourTracker();
 
@@ -54,7 +54,7 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inv )
         {
             ItemStack stack = inv.getStackInSlot( i );
 
-            if( stack == null ) continue;
+            if( stack.isEmpty() ) continue;
 
             if( stack.getItem() instanceof IColouredItem )
             {
@@ -70,9 +70,9 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inv )
             }
         }
 
-        if( colourable == null )
+        if( colourable.isEmpty() )
         {
-            return null;
+            return ItemStack.EMPTY;
         }
 
         return ((IColouredItem) colourable.getItem()).setColour( colourable, tracker.getColour() );
@@ -84,22 +84,22 @@ public int getRecipeSize()
         return 2;
     }
 
-    @Nullable
+    @Nonnull
     @Override
     public ItemStack getRecipeOutput()
     {
-        return null;
+        return ItemStack.EMPTY;
     }
 
     @Nonnull
     @Override
-    public ItemStack[] getRemainingItems( @Nonnull InventoryCrafting inv )
+    public NonNullList<ItemStack> getRemainingItems( @Nonnull InventoryCrafting inventoryCrafting )
     {
-        ItemStack[] results = new ItemStack[ inv.getSizeInventory() ];
-        for( int i = 0; i < results.length; ++i )
+        NonNullList<ItemStack> results = NonNullList.withSize( inventoryCrafting.getSizeInventory(), ItemStack.EMPTY );
+        for( int i = 0; i < results.size(); ++i )
         {
-            ItemStack stack = inv.getStackInSlot( i );
-            results[ i ] = ForgeHooks.getContainerItem( stack );
+            ItemStack stack = inventoryCrafting.getStackInSlot( i );
+            results.set( i, ForgeHooks.getContainerItem( stack ) );
         }
         return results;
     }

src/main/java/dan200/computercraft/shared/common/TileGeneric.java

@@ -34,7 +34,7 @@ public TileGeneric()
 
     public void requestTileEntityUpdate()
     {
-        if( worldObj.isRemote )
+        if( getWorld().isRemote )
         {
             ComputerCraftPacket packet = new ComputerCraftPacket();
             packet.m_packetType = ComputerCraftPacket.RequestTileEntityUpdate;
@@ -52,7 +52,7 @@ public void destroy()
     @Nullable
     public BlockGeneric getBlock()
     {
-        Block block = worldObj.getBlockState( getPos() ).getBlock();
+        Block block = getWorld().getBlockState( getPos() ).getBlock();
         if( block != null && block instanceof BlockGeneric )
         {
             return (BlockGeneric)block;
@@ -62,21 +62,21 @@ public BlockGeneric getBlock()
 
     protected final IBlockState getBlockState()
     {
-        return worldObj.getBlockState( getPos() );
+        return getWorld().getBlockState( getPos() );
     }
 
     public final void updateBlock()
     {
         markDirty();
         BlockPos pos = getPos();
-        IBlockState state = worldObj.getBlockState( pos );
-        worldObj.markBlockRangeForRenderUpdate( pos, pos );
-        worldObj.notifyBlockUpdate( getPos(), state, state, 3 );
+        IBlockState state = getWorld().getBlockState( pos );
+        getWorld().markBlockRangeForRenderUpdate( pos, pos );
+        getWorld().notifyBlockUpdate( getPos(), state, state, 3 );
     }
 
     protected final void setBlockState( IBlockState newState )
     {
-        worldObj.setBlockState( getPos(), newState, 3 );
+        getWorld().setBlockState( getPos(), newState, 3 );
     }
 
     public void getDroppedItems( @Nonnull List<ItemStack> drops, boolean creative )
@@ -151,13 +151,13 @@ public boolean isUsable( EntityPlayer player, boolean ignoreRange )
     {
         if( player != null && player.isEntityAlive() )
         {
-            if( worldObj.getTileEntity( getPos() ) == this )
+            if( getWorld().getTileEntity( getPos() ) == this )
             {
                 if( !ignoreRange )
                 {
                     double range = getInteractRange( player );
                     BlockPos pos = getPos();
-                    return player.getEntityWorld() == worldObj &&
+                    return player.getEntityWorld() == getWorld() &&
                            player.getDistanceSq( (double)pos.getX() + 0.5, (double)pos.getY() + 0.5, (double)pos.getZ() + 0.5 ) <= ( range * range );
                 }
                 return true;
@@ -181,7 +181,7 @@ public final void sendBlockEvent( int eventID )
 
     public final void sendBlockEvent( int eventID, int eventParameter )
     {
-        worldObj.addBlockEvent( getPos(), worldObj.getBlockState( getPos() ).getBlock(), eventID, eventParameter );
+        getWorld().addBlockEvent( getPos(), getWorld().getBlockState( getPos() ).getBlock(), eventID, eventParameter );
     }
 
     public void onBlockEvent( int eventID, int eventParameter )

src/main/java/dan200/computercraft/shared/computer/blocks/BlockCommandComputer.java

@@ -132,13 +132,13 @@ protected TileComputer createTile( ComputerFamily family )
     }
 
     @Override
-    public void onBlockPlacedBy( World world, BlockPos pos, IBlockState state, EntityLivingBase player, ItemStack itemstack )
+    public void onBlockPlacedBy( World world, BlockPos pos, IBlockState state, EntityLivingBase player, @Nonnull ItemStack itemstack )
     {
         // Not sure why this is necessary
         TileEntity tile = world.getTileEntity( pos );
         if( tile != null && tile instanceof TileCommandComputer )
         {
-            tile.setWorldObj( world ); // Not sure why this is necessary
+            tile.setWorld( world ); // Not sure why this is necessary
             tile.setPos( pos ); // Not sure why this is necessary
         }
 

src/main/java/dan200/computercraft/shared/computer/blocks/BlockComputer.java

@@ -164,13 +164,13 @@ protected TileComputer createTile( ComputerFamily family )
     }
 
     @Override
-    public void onBlockPlacedBy( World world, BlockPos pos, IBlockState state, EntityLivingBase player, ItemStack stack )
+    public void onBlockPlacedBy( World world, BlockPos pos, IBlockState state, EntityLivingBase player, @Nonnull ItemStack stack )
     {
         // Not sure why this is necessary
         TileEntity tile = world.getTileEntity( pos );
         if( tile != null && tile instanceof TileComputer )
         {
-            tile.setWorldObj( world ); // Not sure why this is necessary
+            tile.setWorld( world ); // Not sure why this is necessary
             tile.setPos( pos ); // Not sure why this is necessary
         }
 

src/main/java/dan200/computercraft/shared/computer/blocks/TileCommandComputer.java

@@ -70,13 +70,13 @@ public ITextComponent getDisplayName()
         }
 
         @Override
-        public void addChatMessage( @Nonnull ITextComponent chatComponent )
+        public void sendMessage( @Nonnull ITextComponent chatComponent )
         {
             m_outputTable.put( m_outputTable.size() + 1, chatComponent.getUnformattedText() );
         }
 
         @Override
-        public boolean canCommandSenderUseCommand( int level, String command )
+        public boolean canUseCommand( int level, String command )
         {
             return level <= 2;
         }
@@ -179,7 +179,7 @@ public boolean isUsable( EntityPlayer player, boolean ignoreRange )
         MinecraftServer server = player.getServer();
         if( server == null || !server.isCommandBlockEnabled() )
         {
-            player.addChatMessage( new TextComponentTranslation( "advMode.notEnabled" ) );
+            player.sendMessage( new TextComponentTranslation( "advMode.notEnabled" ) );
             return false;
         }
         else if( ComputerCraft.canPlayerUseCommands( player ) && player.capabilities.isCreativeMode )
@@ -188,7 +188,7 @@ else if( ComputerCraft.canPlayerUseCommands( player ) && player.capabilities.isC
         }
         else
         {
-            player.addChatMessage( new TextComponentTranslation( "advMode.notAllowed" ) );
+            player.sendMessage( new TextComponentTranslation( "advMode.notAllowed" ) );
             return false;
         }
     }

src/main/java/dan200/computercraft/shared/computer/blocks/TileComputer.java

@@ -35,7 +35,7 @@ protected ServerComputer createComputer( int instanceID, int id )
     {
         ComputerFamily family = getFamily();
         ServerComputer computer = new ServerComputer(
-            worldObj,
+            getWorld(),
             id,
             m_label,
             instanceID,

src/main/java/dan200/computercraft/shared/computer/blocks/TileComputerBase.java

@@ -62,7 +62,7 @@ protected void unload()
     {
         if( m_instanceID >= 0 )
         {
-            if( !worldObj.isRemote )
+            if( !getWorld().isRemote )
             {
                 ComputerCraft.serverComputerRegistry.remove( m_instanceID );
             }
@@ -76,7 +76,7 @@ public void destroy()
         unload();
         for( EnumFacing dir : EnumFacing.VALUES )
         {
-            RedstoneUtil.propogateRedstoneOutput( worldObj, getPos(), dir );
+            RedstoneUtil.propogateRedstoneOutput( getWorld(), getPos(), dir );
         }
     }
 
@@ -102,7 +102,7 @@ protected boolean canNameWithTag( EntityPlayer player )
 
     protected boolean onDefaultComputerInteract( EntityPlayer player )
     {
-        if( !worldObj.isRemote )
+        if( !getWorld().isRemote )
         {
             if( isUsable( player, false ) )
             {
@@ -117,10 +117,10 @@ protected boolean onDefaultComputerInteract( EntityPlayer player )
     public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, float hitY, float hitZ )
     {
         ItemStack currentItem = player.getHeldItem( EnumHand.MAIN_HAND );
-        if( currentItem != null && currentItem.getItem() == Items.NAME_TAG && canNameWithTag( player ) )
+        if( !currentItem.isEmpty() && currentItem.getItem() == Items.NAME_TAG && canNameWithTag( player ) )
         {
             // Label to rename computer
-            if( !worldObj.isRemote )
+            if( !getWorld().isRemote )
             {
                 if( currentItem.hasDisplayName() )
                 {
@@ -130,7 +130,7 @@ public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, flo
                 {
                     setLabel( null );
                 }
-                currentItem.stackSize--;
+                currentItem.shrink( 1 );
             }
             return true;
         }
@@ -156,7 +156,7 @@ public int getRedstoneOutput( EnumFacing side )
         int localDir = remapLocalSide( DirectionUtil.toLocal( this, side ) );
         if( !isRedstoneBlockedOnSide( localDir ) )
         {
-            if( worldObj != null && !worldObj.isRemote )
+            if( getWorld() != null && !getWorld().isRemote )
             {
                 ServerComputer computer = getServerComputer();
                 if( computer != null )
@@ -181,7 +181,7 @@ public int getBundledRedstoneOutput( @Nonnull EnumFacing side )
         int localDir = remapLocalSide( DirectionUtil.toLocal( this, side ) );
         if( !isRedstoneBlockedOnSide( localDir ) )
         {
-            if( !worldObj.isRemote )
+            if( !getWorld().isRemote )
             {
                 ServerComputer computer = getServerComputer();
                 if( computer != null )
@@ -208,7 +208,7 @@ public void onNeighbourTileEntityChange( @Nonnull BlockPos neighbour )
     @Override
     public void update()
     {
-        if( !worldObj.isRemote )
+        if( !getWorld().isRemote )
         {
             ServerComputer computer = createServerComputer();
             if( computer != null )
@@ -323,18 +323,18 @@ private void updateSideInput( ServerComputer computer, EnumFacing dir, BlockPos
         int localDir = remapLocalSide( DirectionUtil.toLocal( this, dir ) );
         if( !isRedstoneBlockedOnSide( localDir ) )
         {
-            computer.setRedstoneInput( localDir, RedstoneUtil.getRedstoneOutput( worldObj, offset, offsetSide ) );
-            computer.setBundledRedstoneInput( localDir, RedstoneUtil.getBundledRedstoneOutput( worldObj, offset, offsetSide ) );
+            computer.setRedstoneInput( localDir, RedstoneUtil.getRedstoneOutput( getWorld(), offset, offsetSide ) );
+            computer.setBundledRedstoneInput( localDir, RedstoneUtil.getBundledRedstoneOutput( getWorld(), offset, offsetSide ) );
         }
         if( !isPeripheralBlockedOnSide( localDir ) )
         {
-            computer.setPeripheral( localDir, PeripheralUtil.getPeripheral( worldObj, offset, offsetSide ) );
+            computer.setPeripheral( localDir, PeripheralUtil.getPeripheral( getWorld(), offset, offsetSide ) );
         }
     }
 
     public void updateInput()
     {
-        if( worldObj == null || worldObj.isRemote )
+        if( getWorld() == null || getWorld().isRemote )
         {
             return;
         }
@@ -353,7 +353,7 @@ public void updateInput()
 
     public void updateInput( BlockPos neighbour )
     {
-        if( worldObj == null || worldObj.isRemote )
+        if( getWorld() == null || getWorld().isRemote )
         {
             return;
         }
@@ -380,7 +380,7 @@ public void updateOutput()
         updateBlock();
         for( EnumFacing dir : EnumFacing.VALUES )
         {
-            RedstoneUtil.propogateRedstoneOutput( worldObj, getPos(), dir );
+            RedstoneUtil.propogateRedstoneOutput( getWorld(), getPos(), dir );
         }
     }
 
@@ -399,7 +399,7 @@ public ITerminal getTerminal()
     @Override
     public void setComputerID( int id )
     {
-        if( !worldObj.isRemote && m_computerID != id )
+        if( !getWorld().isRemote && m_computerID != id )
         {
             m_computerID = id;
             ServerComputer computer = getServerComputer();
@@ -414,7 +414,7 @@ public void setComputerID( int id )
     @Override
     public void setLabel( String label )
     {
-        if( !worldObj.isRemote )
+        if( !getWorld().isRemote )
         {
             createServerComputer().setLabel( label );
         }
@@ -423,7 +423,7 @@ public void setLabel( String label )
     @Override
     public IComputer createComputer()
     {
-        if( worldObj.isRemote )
+        if( getWorld().isRemote )
         {
             return createClientComputer();
         }
@@ -436,7 +436,7 @@ public IComputer createComputer()
     @Override
     public IComputer getComputer()
     {
-        if( worldObj.isRemote )
+        if( getWorld().isRemote )
         {
             return getClientComputer();
         }
@@ -452,14 +452,14 @@ public ComputerFamily getFamily()
         BlockComputerBase block = getBlock();
         if( block != null )
         {
-            return block.getFamily( worldObj, getPos() );
+            return block.getFamily( getWorld(), getPos() );
         }
         return ComputerFamily.Normal;
     }
 
     public ServerComputer createServerComputer()
     {
-        if( !worldObj.isRemote )
+        if( !getWorld().isRemote )
         {
             boolean changed = false;
             if( m_instanceID < 0 )
@@ -485,7 +485,7 @@ public ServerComputer createServerComputer()
 
     public ServerComputer getServerComputer()
     {
-        if( !worldObj.isRemote )
+        if( !getWorld().isRemote )
         {
             return ComputerCraft.serverComputerRegistry.get( m_instanceID );
         }
@@ -494,7 +494,7 @@ public ServerComputer getServerComputer()
 
     public ClientComputer createClientComputer()
     {
-        if( worldObj.isRemote )
+        if( getWorld().isRemote )
         {
             if( m_instanceID >= 0 )
             {
@@ -510,7 +510,7 @@ public ClientComputer createClientComputer()
 
     public ClientComputer getClientComputer()
     {
-        if( worldObj.isRemote )
+        if( getWorld().isRemote )
         {
             return ComputerCraft.clientComputerRegistry.get( m_instanceID );
         }

src/main/java/dan200/computercraft/shared/computer/core/ClientComputer.java

@@ -169,7 +169,7 @@ public void readDescription( NBTTagCompound nbttagcompound )
         m_blinking = nbttagcompound.getBoolean( "blinking" );
         if( nbttagcompound.hasKey( "userData" ) )
         {
-            m_userData = (NBTTagCompound)(nbttagcompound.getCompoundTag( "userData" )).copy();
+            m_userData = nbttagcompound.getCompoundTag( "userData" ).copy();
         }
         else
         {

src/main/java/dan200/computercraft/shared/computer/items/ComputerItemFactory.java

@@ -13,8 +13,11 @@
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 
+import javax.annotation.Nonnull;
+
 public class ComputerItemFactory
 {
+    @Nonnull
     public static ItemStack create( IComputerTile computerTile )
     {
         IComputer computer = computerTile.getComputer();
@@ -30,6 +33,7 @@ public static ItemStack create( IComputerTile computerTile )
         }
     }
 
+    @Nonnull
     public static ItemStack create( int id, String label, ComputerFamily family )
     {
         ItemComputer computer = ((ItemComputer)Item.getItemFromBlock( ComputerCraft.Blocks.computer ));
@@ -46,6 +50,6 @@ public static ItemStack create( int id, String label, ComputerFamily family )
                 return commandComputer.create( id, label, family );
             }
         }
-        return null;
+        return ItemStack.EMPTY;
     }
 }

src/main/java/dan200/computercraft/shared/computer/items/IComputerItem.java

@@ -9,9 +9,11 @@
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 import net.minecraft.item.ItemStack;
 
+import javax.annotation.Nonnull;
+
 public interface IComputerItem
 {
-    int getComputerID( ItemStack stack );
-    String getLabel( ItemStack stack );
-    ComputerFamily getFamily( ItemStack stack );
+    int getComputerID( @Nonnull ItemStack stack );
+    String getLabel( @Nonnull ItemStack stack );
+    ComputerFamily getFamily( @Nonnull ItemStack stack );
 }

src/main/java/dan200/computercraft/shared/computer/items/ItemCommandComputer.java

@@ -13,10 +13,10 @@
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.nbt.NBTTagCompound;
+import net.minecraft.util.NonNullList;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
-import java.util.List;
 
 public class ItemCommandComputer extends ItemComputer
 {
@@ -53,7 +53,7 @@ public ItemStack create( int id, String label, ComputerFamily family )
     }
 
     @Override
-    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull List<ItemStack> list )
+    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull NonNullList<ItemStack> list )
     {
         list.add( ComputerItemFactory.create( -1, null, ComputerFamily.Command ) );
     }
@@ -61,7 +61,7 @@ public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Non
     // IComputerItem implementation
 
     @Override
-    public int getComputerID( ItemStack stack )
+    public int getComputerID( @Nonnull ItemStack stack )
     {
         if( stack.hasTagCompound() && stack.getTagCompound().hasKey( "computerID" ) )
         {

src/main/java/dan200/computercraft/shared/computer/items/ItemComputer.java

@@ -17,13 +17,13 @@
 import net.minecraft.item.ItemStack;
 import net.minecraft.nbt.NBTTagCompound;
 import net.minecraft.tileentity.TileEntity;
-import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.EnumFacing;
+import net.minecraft.util.NonNullList;
+import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
-import java.util.List;
 
 public class ItemComputer extends ItemComputerBase
 {
@@ -73,7 +73,7 @@ public ItemStack create( int id, String label, ComputerFamily family )
     }
 
     @Override
-    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull List<ItemStack> list )
+    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull NonNullList<ItemStack> list )
     {
         list.add( ComputerItemFactory.create( -1, null, ComputerFamily.Normal ) );
         list.add( ComputerItemFactory.create( -1, null, ComputerFamily.Advanced ) );
@@ -95,7 +95,7 @@ public boolean placeBlockAt( @Nonnull ItemStack stack, @Nonnull EntityPlayer pla
         return false;
     }
 
-    private void setupComputerAfterPlacement( ItemStack stack, IComputerTile computer )
+    private void setupComputerAfterPlacement( @Nonnull ItemStack stack, IComputerTile computer )
     {
         // Set ID
         int id = getComputerID( stack );
@@ -114,7 +114,7 @@ private void setupComputerAfterPlacement( ItemStack stack, IComputerTile compute
 
     @Nonnull
     @Override
-    public String getUnlocalizedName( ItemStack stack )
+    public String getUnlocalizedName( @Nonnull ItemStack stack )
     {
         switch( getFamily( stack ) )
         {
@@ -137,7 +137,7 @@ public String getUnlocalizedName( ItemStack stack )
     // IComputerItem implementation
 
     @Override
-    public int getComputerID( ItemStack stack )
+    public int getComputerID( @Nonnull ItemStack stack )
     {
         if( stack.hasTagCompound() && stack.getTagCompound().hasKey( "computerID" ) )
         {

src/main/java/dan200/computercraft/shared/computer/items/ItemComputerBase.java

@@ -51,7 +51,7 @@ public void addInformation( @Nonnull ItemStack stack, @Nonnull EntityPlayer play
     // IComputerItem implementation
 
     @Override
-    public abstract int getComputerID( ItemStack stack );
+    public abstract int getComputerID( @Nonnull ItemStack stack );
 
     @Override
     public String getLabel( @Nonnull ItemStack stack )
@@ -64,7 +64,7 @@ public String getLabel( @Nonnull ItemStack stack )
     }
 
     @Override
-    public final ComputerFamily getFamily( ItemStack stack )
+    public final ComputerFamily getFamily( @Nonnull ItemStack stack )
     {
         int damage = stack.getItemDamage();
         return getFamily( damage );

src/main/java/dan200/computercraft/shared/media/inventory/ContainerHeldItem.java

@@ -25,6 +25,7 @@ public ContainerHeldItem( EntityPlayer player, EnumHand hand )
         m_stack = InventoryUtil.copyItem( player.getHeldItem( hand ) );
     }
 
+    @Nonnull
     public ItemStack getStack()
     {
         return m_stack;
@@ -36,7 +37,7 @@ public boolean canInteractWith( @Nonnull EntityPlayer player )
         if( player != null && player.isEntityAlive() )
         {
             ItemStack stack = player.getHeldItem( m_hand );
-            if( (stack == m_stack) || (stack != null && m_stack != null && stack.getItem() == m_stack.getItem()) )
+            if( (stack == m_stack) || (!stack.isEmpty() && !m_stack.isEmpty() && stack.getItem() == m_stack.getItem()) )
             {
                 return true;
             }

src/main/java/dan200/computercraft/shared/media/items/ItemDiskExpanded.java

@@ -11,12 +11,15 @@
 import net.minecraft.item.ItemStack;
 import net.minecraft.nbt.NBTTagCompound;
 
+import javax.annotation.Nonnull;
+
 public class ItemDiskExpanded extends ItemDiskLegacy
 {    
     public ItemDiskExpanded()
     {
     }
 
+    @Nonnull
     public static ItemStack createFromIDAndColour( int id, String label, int colour )
     {
         ItemStack stack = new ItemStack( ComputerCraft.Items.diskExpanded, 1, 0 );
@@ -34,7 +37,7 @@ public static ItemStack createFromIDAndColour( int id, String label, int colour
     }
     
     @Override    
-    public int getDiskID( ItemStack stack )
+    public int getDiskID( @Nonnull ItemStack stack )
     {
         NBTTagCompound nbt = stack.getTagCompound();
         if( nbt != null && nbt.hasKey( "diskID" ) )
@@ -45,7 +48,7 @@ public int getDiskID( ItemStack stack )
     }
 
     @Override
-    protected void setDiskID( ItemStack stack, int id )
+    protected void setDiskID( @Nonnull ItemStack stack, int id )
     {
         if( id >= 0 )
         {
@@ -60,7 +63,7 @@ protected void setDiskID( ItemStack stack, int id )
     }
 
     @Override
-    public int getColour( ItemStack stack )
+    public int getColour( @Nonnull ItemStack stack )
     {
         NBTTagCompound nbt = stack.getTagCompound();
         if( nbt != null && nbt.hasKey( "color" ) )

src/main/java/dan200/computercraft/shared/media/items/ItemDiskLegacy.java

@@ -16,6 +16,7 @@
 import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
+import net.minecraft.util.NonNullList;
 import net.minecraft.util.SoundEvent;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.IBlockAccess;
@@ -36,7 +37,7 @@ public ItemDiskLegacy()
     }
     
     @Override
-    public void getSubItems( @Nonnull Item itemID, CreativeTabs tabs, List<ItemStack> list )
+    public void getSubItems( @Nonnull Item itemID, CreativeTabs tabs, NonNullList<ItemStack> list )
     {
         for( int colour=0; colour<16; ++colour )
         {
@@ -47,7 +48,8 @@ public void getSubItems( @Nonnull Item itemID, CreativeTabs tabs, List<ItemStack
             }
         }
     }
-            
+
+    @Nonnull
     public static ItemStack createFromIDAndColour( int id, String label, int colour )
     {
         if( colour != Colour.Blue.getHex() )
@@ -61,7 +63,7 @@ public static ItemStack createFromIDAndColour( int id, String label, int colour
         return stack;
     }
     
-    public int getDiskID( ItemStack stack )
+    public int getDiskID( @Nonnull ItemStack stack )
     {
         int damage = stack.getItemDamage();
         if( damage > 0 )
@@ -71,7 +73,7 @@ public int getDiskID( ItemStack stack )
         return -1;
     }
 
-    protected void setDiskID( ItemStack stack, int id )
+    protected void setDiskID( @Nonnull ItemStack stack, int id )
     {
         if( id > 0 ) {
             stack.setItemDamage( id );
@@ -81,7 +83,7 @@ protected void setDiskID( ItemStack stack, int id )
     }
 
     @Override
-    public void addInformation( ItemStack stack, EntityPlayer player, List<String> list, boolean debug )
+    public void addInformation( @Nonnull ItemStack stack, EntityPlayer player, List<String> list, boolean debug )
     {
         if( debug )
         {
@@ -144,13 +146,13 @@ public IMount createDataMount( @Nonnull ItemStack stack, @Nonnull World world )
     }
 
     @Override
-    public int getColour( ItemStack stack )
+    public int getColour( @Nonnull ItemStack stack )
     {
         return Colour.Blue.getHex();
     }
 
     @Override
-    public boolean doesSneakBypassUse( ItemStack stack, IBlockAccess world, BlockPos pos, EntityPlayer player )
+    public boolean doesSneakBypassUse( @Nonnull ItemStack stack, IBlockAccess world, BlockPos pos, EntityPlayer player )
     {
         return true;
     }

src/main/java/dan200/computercraft/shared/media/items/ItemPrintout.java

@@ -15,6 +15,7 @@
 import net.minecraft.util.ActionResult;
 import net.minecraft.util.EnumActionResult;
 import net.minecraft.util.EnumHand;
+import net.minecraft.util.NonNullList;
 import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
@@ -42,7 +43,7 @@ public ItemPrintout()
     }
 
     @Override
-    public void getSubItems( @Nonnull Item itemID, CreativeTabs tabs, List<ItemStack> list )
+    public void getSubItems( @Nonnull Item itemID, CreativeTabs tabs, NonNullList<ItemStack> list )
     {
         list.add( createSingleFromTitleAndText( null, new String[ LINES_PER_PAGE ], new String[ LINES_PER_PAGE ] ) );
         list.add( createMultipleFromTitleAndText( null, new String[ 2*LINES_PER_PAGE ], new String[ 2*LINES_PER_PAGE ] ) );
@@ -50,7 +51,7 @@ public void getSubItems( @Nonnull Item itemID, CreativeTabs tabs, List<ItemStack
     }
 
     @Override
-    public void addInformation( ItemStack itemstack, EntityPlayer par2EntityPlayer, List<String> list, boolean flag )
+    public void addInformation( @Nonnull ItemStack itemstack, EntityPlayer par2EntityPlayer, List<String> list, boolean flag )
     {
         String title = getTitle( itemstack );
         if( title != null && title.length() > 0 )
@@ -61,7 +62,7 @@ public void addInformation( ItemStack itemstack, EntityPlayer par2EntityPlayer,
 
     @Nonnull
     @Override
-    public String getUnlocalizedName( ItemStack stack )
+    public String getUnlocalizedName( @Nonnull ItemStack stack )
     {
         Type type = getType( stack );
         switch( type )
@@ -84,15 +85,16 @@ public String getUnlocalizedName( ItemStack stack )
 
     @Nonnull
     @Override
-    public ActionResult<ItemStack> onItemRightClick( @Nonnull ItemStack stack, World world, EntityPlayer player, EnumHand hand )
+    public ActionResult<ItemStack> onItemRightClick( World world, EntityPlayer player, @Nonnull EnumHand hand )
     {
         if( !world.isRemote )
         {
             ComputerCraft.openPrintoutGUI( player, hand );
         }
-        return new ActionResult<ItemStack>( EnumActionResult.SUCCESS, stack );
+        return new ActionResult<ItemStack>( EnumActionResult.SUCCESS, player.getHeldItem( hand ) );
     }
 
+    @Nonnull
     private static ItemStack createFromTitleAndText( Type type, String title, String[] text, String[] colours )
     {
         // Calculate damage
@@ -153,22 +155,25 @@ private static ItemStack createFromTitleAndText( Type type, String title, String
         return stack;
     }
 
+    @Nonnull
     public static ItemStack createSingleFromTitleAndText( String title, String[] text, String[] colours )
     {
         return createFromTitleAndText( Type.Single, title, text, colours );
     }
 
+    @Nonnull
     public static ItemStack createMultipleFromTitleAndText( String title, String[] text, String[] colours )
     {
         return createFromTitleAndText( Type.Multiple, title, text, colours );
     }
 
+    @Nonnull
     public static ItemStack createBookFromTitleAndText( String title, String[] text, String[] colours )
     {
         return createFromTitleAndText( Type.Book, title, text, colours );
     }
 
-    public static Type getType( ItemStack stack )
+    public static Type getType( @Nonnull ItemStack stack )
     {
         int damage = stack.getItemDamage();
         switch( damage )
@@ -189,7 +194,7 @@ public static Type getType( ItemStack stack )
         }
     }
 
-    public static String getTitle( ItemStack stack )
+    public static String getTitle( @Nonnull ItemStack stack )
     {
         NBTTagCompound nbt = stack.getTagCompound();
         if( nbt != null && nbt.hasKey( "title" ) )
@@ -199,7 +204,7 @@ public static String getTitle( ItemStack stack )
         return null;
     }
 
-    public static int getPageCount( ItemStack stack )
+    public static int getPageCount( @Nonnull ItemStack stack )
     {
         NBTTagCompound nbt = stack.getTagCompound();
         if( nbt != null && nbt.hasKey( "pages" ) )
@@ -209,7 +214,7 @@ public static int getPageCount( ItemStack stack )
         return 1;
     }
 
-    public static String[] getText( ItemStack stack )
+    public static String[] getText( @Nonnull ItemStack stack )
     {
         NBTTagCompound nbt = stack.getTagCompound();
         int numLines = getPageCount( stack ) * LINES_PER_PAGE;
@@ -228,7 +233,7 @@ public static String[] getText( ItemStack stack )
         return lines;
     }
 
-    public static String[] getColours( ItemStack stack )
+    public static String[] getColours( @Nonnull ItemStack stack )
     {
         NBTTagCompound nbt = stack.getTagCompound();
         int numLines = getPageCount( stack ) * LINES_PER_PAGE;

src/main/java/dan200/computercraft/shared/media/items/ItemTreasureDisk.java

@@ -16,6 +16,7 @@
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.nbt.NBTTagCompound;
+import net.minecraft.util.NonNullList;
 import net.minecraft.util.SoundEvent;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.IBlockAccess;
@@ -36,12 +37,12 @@ public ItemTreasureDisk()
     }
     
     @Override
-    public void getSubItems( @Nonnull Item itemID, CreativeTabs tabs, List<ItemStack> list )
+    public void getSubItems( @Nonnull Item itemID, CreativeTabs tabs, NonNullList<ItemStack> list )
     {
     }
     
     @Override
-    public void addInformation( ItemStack stack, EntityPlayer player, List<String> list, boolean bool )
+    public void addInformation( @Nonnull ItemStack stack, EntityPlayer player, List<String> list, boolean bool )
     {
         String label = getTitle( stack );
         if( label != null && label.length() > 0 )
@@ -51,7 +52,7 @@ public void addInformation( ItemStack stack, EntityPlayer player, List<String> l
     }
 
     @Override
-    public boolean doesSneakBypassUse( ItemStack stack, IBlockAccess world, BlockPos pos, EntityPlayer player )
+    public boolean doesSneakBypassUse( @Nonnull ItemStack stack, IBlockAccess world, BlockPos pos, EntityPlayer player )
     {
         return true;
     }
@@ -138,7 +139,7 @@ private static IMount getTreasureMount()
 
     // private stuff
     
-    public String getTitle( ItemStack stack )
+    public String getTitle( @Nonnull ItemStack stack )
     {
         NBTTagCompound nbt = stack.getTagCompound();
         if( nbt != null && nbt.hasKey( "title" ) )
@@ -148,7 +149,7 @@ public String getTitle( ItemStack stack )
         return "'alongtimeago' by dan200";
     }
     
-    public String getSubPath( ItemStack stack )
+    public String getSubPath( @Nonnull ItemStack stack )
     {
         NBTTagCompound nbt = stack.getTagCompound();
         if( nbt != null && nbt.hasKey( "subPath" ) )
@@ -158,7 +159,7 @@ public String getSubPath( ItemStack stack )
         return "dan200/alongtimeago";
     }
     
-    public int getColour( ItemStack stack )
+    public int getColour( @Nonnull ItemStack stack )
     {
         NBTTagCompound nbt = stack.getTagCompound();
         if( nbt != null && nbt.hasKey( "colour" ) )

src/main/java/dan200/computercraft/shared/media/recipes/DiskRecipe.java

@@ -14,7 +14,9 @@
 import net.minecraft.inventory.InventoryCrafting;
 import net.minecraft.item.ItemStack;
 import net.minecraft.item.crafting.IRecipe;
+import net.minecraft.util.NonNullList;
 import net.minecraft.world.World;
+import net.minecraftforge.common.ForgeHooks;
 
 import javax.annotation.Nonnull;
 
@@ -30,7 +32,7 @@ public boolean matches( @Nonnull InventoryCrafting inv, @Nonnull World world )
         {
             ItemStack stack = inv.getStackInSlot( i );
 
-            if( stack != null )
+            if( !stack.isEmpty() )
             {
                 if( stack.getItem() == Items.PAPER )
                 {
@@ -52,6 +54,7 @@ else if( ColourUtils.getStackColour( stack ) < 0 )
         return redstoneFound && paperFound;
     }
 
+    @Nonnull
     @Override
     public ItemStack getCraftingResult( @Nonnull InventoryCrafting inv )
     {
@@ -61,8 +64,8 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inv )
         {
             ItemStack stack = inv.getStackInSlot( i );
 
-            if( stack == null ) continue;
-
+            if( stack.isEmpty() ) continue;
+            
             if( stack.getItem() != Items.PAPER && stack.getItem() != Items.REDSTONE )
             {
                 int index = ColourUtils.getStackColour( stack );
@@ -82,6 +85,7 @@ public int getRecipeSize()
         return 2;
     }
 
+    @Nonnull
     @Override
     public ItemStack getRecipeOutput()
     {
@@ -90,13 +94,13 @@ public ItemStack getRecipeOutput()
 
     @Nonnull
     @Override
-    public ItemStack[] getRemainingItems( @Nonnull InventoryCrafting inv )
+    public NonNullList<ItemStack> getRemainingItems( @Nonnull InventoryCrafting inventoryCrafting )
     {
-        ItemStack[] results = new ItemStack[ inv.getSizeInventory() ];
-        for( int i = 0; i < results.length; ++i )
+        NonNullList<ItemStack> results = NonNullList.withSize( inventoryCrafting.getSizeInventory(), ItemStack.EMPTY );
+        for( int i = 0; i < results.size(); ++i )
         {
-            ItemStack stack = inv.getStackInSlot( i );
-            results[ i ] = net.minecraftforge.common.ForgeHooks.getContainerItem( stack );
+            ItemStack stack = inventoryCrafting.getStackInSlot( i );
+            results.set( i, ForgeHooks.getContainerItem( stack ) );
         }
         return results;
     }

src/main/java/dan200/computercraft/shared/media/recipes/PrintoutRecipe.java

@@ -12,7 +12,9 @@
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.item.crafting.IRecipe;
+import net.minecraft.util.NonNullList;
 import net.minecraft.world.World;
+import net.minecraftforge.common.ForgeHooks;
 
 import javax.annotation.Nonnull;
 
@@ -28,6 +30,7 @@ public int getRecipeSize()
         return 3;
     }
     
+    @Nonnull
     @Override
     public ItemStack getRecipeOutput()
     {
@@ -37,9 +40,10 @@ public ItemStack getRecipeOutput()
     @Override
     public boolean matches( @Nonnull InventoryCrafting _inventory, @Nonnull World world )
     {
-        return (getCraftingResult( _inventory ) != null);
+        return !getCraftingResult( _inventory ).isEmpty();
     }
 
+    @Nonnull
     @Override
     public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
     {
@@ -55,7 +59,7 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
             for( int x=0; x<inventory.getWidth(); ++x )
             {
                 ItemStack stack = inventory.getStackInRowAndColumn(x, y);
-                if( stack != null )
+                if( !stack.isEmpty() )
                 {
                     Item item = stack.getItem();
                     if( item instanceof ItemPrintout && ItemPrintout.getType( stack ) != ItemPrintout.Type.Book )
@@ -89,7 +93,7 @@ else if( item == Items.LEATHER && !leatherFound )
                     }
                     else
                     {
-                        return null;
+                        return ItemStack.EMPTY;
                     }
                 }
             }
@@ -145,18 +149,18 @@ else if( item == Items.LEATHER && !leatherFound )
             }
         }
 
-        return null;
+        return ItemStack.EMPTY;
     }
 
     @Nonnull
     @Override
-    public ItemStack[] getRemainingItems( @Nonnull InventoryCrafting inventoryCrafting )
+    public NonNullList<ItemStack> getRemainingItems( @Nonnull InventoryCrafting inventoryCrafting )
     {
-        ItemStack[] results = new ItemStack[ inventoryCrafting.getSizeInventory() ];
-        for (int i = 0; i < results.length; ++i)
+        NonNullList<ItemStack> results = NonNullList.withSize( inventoryCrafting.getSizeInventory(), ItemStack.EMPTY );
+        for( int i = 0; i < results.size(); ++i )
         {
-            ItemStack stack = inventoryCrafting.getStackInSlot(i);
-            results[i] = net.minecraftforge.common.ForgeHooks.getContainerItem(stack);
+            ItemStack stack = inventoryCrafting.getStackInSlot( i );
+            results.set( i, ForgeHooks.getContainerItem( stack ) );
         }
         return results;
     }

src/main/java/dan200/computercraft/shared/peripheral/common/BlockPeripheral.java

@@ -554,13 +554,13 @@ public TilePeripheralBase createTile( PeripheralType type )
     }
 
     @Override
-    public void onBlockPlacedBy( World world, BlockPos pos, IBlockState state, EntityLivingBase player, ItemStack stack )
+    public void onBlockPlacedBy( World world, BlockPos pos, IBlockState state, EntityLivingBase player, @Nonnull ItemStack stack )
     {
         // Not sure why this is necessary
         TileEntity tile = world.getTileEntity( pos );
         if( tile != null && tile instanceof TilePeripheralBase )
         {
-            tile.setWorldObj( world ); // Not sure why this is necessary
+            tile.setWorld( world ); // Not sure why this is necessary
             tile.setPos( pos ); // Not sure why this is necessary
         }
 

src/main/java/dan200/computercraft/shared/peripheral/common/IPeripheralItem.java

@@ -9,7 +9,9 @@
 import dan200.computercraft.shared.peripheral.PeripheralType;
 import net.minecraft.item.ItemStack;
 
+import javax.annotation.Nonnull;
+
 public interface IPeripheralItem
 {
-    PeripheralType getPeripheralType( ItemStack stack );
+    PeripheralType getPeripheralType( @Nonnull ItemStack stack );
 }

src/main/java/dan200/computercraft/shared/peripheral/common/ItemAdvancedModem.java

@@ -12,10 +12,10 @@
 import net.minecraft.creativetab.CreativeTabs;
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
+import net.minecraft.util.NonNullList;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
-import java.util.List;
 
 public class ItemAdvancedModem extends ItemPeripheralBase
 {
@@ -26,6 +26,7 @@ public ItemAdvancedModem( Block block )
         setCreativeTab( ComputerCraft.mainCreativeTab );
     }
 
+    @Nonnull
     public ItemStack create( PeripheralType type, String label, int quantity )
     {
         ItemStack stack;
@@ -39,7 +40,7 @@ public ItemStack create( PeripheralType type, String label, int quantity )
             default:
             {
                 // Ignore types we can't handle
-                return null;
+                return ItemStack.EMPTY;
             }
         }
         if( label != null )
@@ -50,7 +51,7 @@ public ItemStack create( PeripheralType type, String label, int quantity )
     }
 
     @Override
-    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull List<ItemStack> list )
+    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull NonNullList<ItemStack> list )
     {
         list.add( PeripheralItemFactory.create( PeripheralType.AdvancedModem, null, 1 ) );
     }

src/main/java/dan200/computercraft/shared/peripheral/common/ItemCable.java

@@ -16,16 +16,12 @@
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.tileentity.TileEntity;
-import net.minecraft.util.EnumActionResult;
-import net.minecraft.util.EnumHand;
-import net.minecraft.util.SoundCategory;
+import net.minecraft.util.*;
 import net.minecraft.util.math.BlockPos;
-import net.minecraft.util.EnumFacing;
 import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
-import java.util.List;
 
 public class ItemCable extends ItemPeripheralBase
 {
@@ -36,6 +32,7 @@ public ItemCable( Block block )
         setCreativeTab( ComputerCraft.mainCreativeTab );
     }
 
+    @Nonnull
     public ItemStack create( PeripheralType type, String label, int quantity )
     {
         ItemStack stack;
@@ -53,7 +50,7 @@ public ItemStack create( PeripheralType type, String label, int quantity )
             }
             default:
             {
-                return null;
+                return ItemStack.EMPTY;
             }
         }
         if( label != null )
@@ -64,7 +61,7 @@ public ItemStack create( PeripheralType type, String label, int quantity )
     }
 
     @Override
-    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull List<ItemStack> list )
+    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull NonNullList<ItemStack> list )
     {
         list.add( PeripheralItemFactory.create( PeripheralType.WiredModem, null, 1 ) );
         list.add( PeripheralItemFactory.create( PeripheralType.Cable, null, 1 ) );
@@ -72,8 +69,9 @@ public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Non
 
     @Nonnull
     @Override
-    public EnumActionResult onItemUse( ItemStack stack, @Nonnull EntityPlayer player, World world, @Nonnull BlockPos pos, EnumHand hand, @Nonnull EnumFacing side, float fx, float fy, float fz )
+    public EnumActionResult onItemUse( @Nonnull EntityPlayer player, World world, @Nonnull BlockPos pos, @Nonnull EnumHand hand, @Nonnull EnumFacing side, float fx, float fy, float fz )
     {
+        ItemStack stack = player.getHeldItem( hand );
         if( !canPlaceBlockOnSide( world, pos, side, player, stack ) )
         {
             return EnumActionResult.FAIL;
@@ -88,11 +86,11 @@ public EnumActionResult onItemUse( ItemStack stack, @Nonnull EntityPlayer player
             PeripheralType existingType = ComputerCraft.Blocks.cable.getPeripheralType( world, pos );
             if( existingType == PeripheralType.WiredModem && type == PeripheralType.Cable )
             {
-                if( stack.stackSize > 0 )
+                if( !stack.isEmpty() )
                 {
                     world.setBlockState( pos, existingState.withProperty( BlockCable.Properties.CABLE, true ), 3 );
                     world.playSound( null, pos.getX() + 0.5, pos.getY() + 0.5, pos.getZ() + 0.5, ComputerCraft.Blocks.cable.getSoundType().getPlaceSound(), SoundCategory.BLOCKS, (ComputerCraft.Blocks.cable.getSoundType().getVolume() + 1.0F ) / 2.0F, ComputerCraft.Blocks.cable.getSoundType().getPitch() * 0.8F);
-                    stack.stackSize--;
+                    stack.shrink( 1 );
                     
                     TileEntity tile = world.getTileEntity( pos );
                     if( tile != null && tile instanceof TileCable )
@@ -118,11 +116,11 @@ public EnumActionResult onItemUse( ItemStack stack, @Nonnull EntityPlayer player
                 PeripheralType offsetExistingType = ComputerCraft.Blocks.cable.getPeripheralType( world, offset );
                 if( offsetExistingType == PeripheralType.Cable && type == PeripheralType.WiredModem )
                 {
-                    if( stack.stackSize > 0 )
+                    if( !stack.isEmpty() )
                     {
                         world.setBlockState( offset, offsetExistingState.withProperty( BlockCable.Properties.MODEM, BlockCableModemVariant.fromFacing( side.getOpposite() ) ), 3 );
                         world.playSound( null, offset.getX() + 0.5, offset.getY() + 0.5, offset.getZ() + 0.5, ComputerCraft.Blocks.cable.getSoundType().getPlaceSound(), SoundCategory.BLOCKS, (ComputerCraft.Blocks.cable.getSoundType().getVolume() + 1.0F ) / 2.0F, ComputerCraft.Blocks.cable.getSoundType().getPitch() * 0.8F);
-                        stack.stackSize--;
+                        stack.shrink( 1 );
 
                         TileEntity tile = world.getTileEntity( offset );
                         if( tile != null && tile instanceof TileCable )
@@ -138,11 +136,11 @@ public EnumActionResult onItemUse( ItemStack stack, @Nonnull EntityPlayer player
                 // Try to add a cable to a modem
                 if( offsetExistingType == PeripheralType.WiredModem && type == PeripheralType.Cable )
                 {
-                    if( stack.stackSize > 0 )
+                    if( !stack.isEmpty() )
                     {
                         world.setBlockState( offset, offsetExistingState.withProperty( BlockCable.Properties.CABLE, true ), 3 );
                         world.playSound( null, offset.getX() + 0.5, offset.getY() + 0.5, offset.getZ() + 0.5, ComputerCraft.Blocks.cable.getSoundType().getPlaceSound(), SoundCategory.BLOCKS, (ComputerCraft.Blocks.cable.getSoundType().getVolume() + 1.0F ) / 2.0F, ComputerCraft.Blocks.cable.getSoundType().getPitch() * 0.8F);
-                        stack.stackSize--;
+                        stack.shrink( 1 );
 
                         TileEntity tile = world.getTileEntity( offset );
                         if( tile != null && tile instanceof TileCable )
@@ -157,7 +155,7 @@ public EnumActionResult onItemUse( ItemStack stack, @Nonnull EntityPlayer player
             }
         }
         
-        return super.onItemUse( stack, player, world, pos, hand, side, fx, fy, fz );
+        return super.onItemUse( player, world, pos, hand, side, fx, fy, fz );
     }
 
     @Override

src/main/java/dan200/computercraft/shared/peripheral/common/ItemPeripheral.java

@@ -12,10 +12,10 @@
 import net.minecraft.creativetab.CreativeTabs;
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
+import net.minecraft.util.NonNullList;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
-import java.util.List;
 
 public class ItemPeripheral extends ItemPeripheralBase
 {
@@ -26,6 +26,7 @@ public ItemPeripheral( Block block )
         setCreativeTab( ComputerCraft.mainCreativeTab );
     }
 
+    @Nonnull
     public ItemStack create( PeripheralType type, String label, int quantity )
     {
         ItemStack stack;
@@ -65,7 +66,7 @@ public ItemStack create( PeripheralType type, String label, int quantity )
             default:
             {
                 // Ignore types we can't handle
-                return null;
+                return ItemStack.EMPTY;
             }
         }
         if( label != null )
@@ -76,7 +77,7 @@ public ItemStack create( PeripheralType type, String label, int quantity )
     }
 
     @Override
-    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull List<ItemStack> list )
+    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull NonNullList<ItemStack> list )
     {
         list.add( PeripheralItemFactory.create( PeripheralType.DiskDrive, null, 1 ) );
         list.add( PeripheralItemFactory.create( PeripheralType.Printer, null, 1 ) );

src/main/java/dan200/computercraft/shared/peripheral/common/ItemPeripheralBase.java

@@ -59,7 +59,7 @@ public boolean canPlaceBlockOnSide( World world, @Nonnull BlockPos pos, @Nonnull
 
     @Nonnull
     @Override
-    public String getUnlocalizedName( ItemStack stack )
+    public String getUnlocalizedName( @Nonnull ItemStack stack )
     {
         PeripheralType type = getPeripheralType( stack );
         switch( type )
@@ -108,7 +108,7 @@ public String getUnlocalizedName( ItemStack stack )
     // IPeripheralItem implementation
 
     @Override
-    public final PeripheralType getPeripheralType( ItemStack stack )
+    public final PeripheralType getPeripheralType( @Nonnull ItemStack stack )
     {
         return getPeripheralType( stack.getItemDamage() );
     }

src/main/java/dan200/computercraft/shared/peripheral/common/PeripheralItemFactory.java

@@ -11,13 +11,17 @@
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 
+import javax.annotation.Nonnull;
+
 public class PeripheralItemFactory
 {
+    @Nonnull
     public static ItemStack create( IPeripheralTile tile )
     {
         return create( tile.getPeripheralType(), tile.getLabel(), 1 );
     }
 
+    @Nonnull
     public static ItemStack create( PeripheralType type, String label, int quantity )
     {
         ItemPeripheral peripheral = ((ItemPeripheral)Item.getItemFromBlock( ComputerCraft.Blocks.peripheral ));
@@ -44,6 +48,6 @@ public static ItemStack create( PeripheralType type, String label, int quantity
                 return advancedModem.create( type, label, quantity );
             }
         }
-        return null;
+        return ItemStack.EMPTY;
     }
 }

src/main/java/dan200/computercraft/shared/peripheral/diskdrive/ContainerDiskDrive.java

@@ -40,46 +40,47 @@ public ContainerDiskDrive( IInventory playerInventory, TileDiskDrive diskDrive )
     @Override
     public boolean canInteractWith( @Nonnull EntityPlayer player )
     {
-        return m_diskDrive.isUseableByPlayer( player );
+        return m_diskDrive.isUsableByPlayer( player );
     }
 
+    @Nonnull
     @Override
     public ItemStack transferStackInSlot( EntityPlayer player, int i )
     {
-        ItemStack itemstack = null;
+        ItemStack itemstack = ItemStack.EMPTY;
         Slot slot = inventorySlots.get(i);
         if(slot != null && slot.getHasStack())
         {
-            ItemStack itemstack1 = slot.getStack();
+            ItemStack itemstack1 = slot.getStack().copy();
             itemstack = itemstack1.copy();
             if(i == 0 )
             {
                 if(!mergeItemStack(itemstack1, 1, 37, true))
                 {
-                    return null;
+                    return ItemStack.EMPTY;
                 }
             }
             else if( !mergeItemStack(itemstack1, 0, 1, false) )
             {
-                return null;
+                return ItemStack.EMPTY;
             }
             
-            if(itemstack1.stackSize == 0)
+            if(itemstack1.isEmpty())
             {
-                slot.putStack(null);
+                slot.putStack(ItemStack.EMPTY);
             }
             else
             {
                 slot.onSlotChanged();
             }
             
-            if(itemstack1.stackSize != itemstack.stackSize)
+            if(itemstack1.getCount() != itemstack.getCount())
             {
-                slot.onPickupFromSlot(player, itemstack1);
+                slot.onTake(player, itemstack1);
             }
             else
             {
-                return null;
+                return ItemStack.EMPTY;
             }
         }
         return itemstack;

src/main/java/dan200/computercraft/shared/peripheral/diskdrive/TileDiskDrive.java

@@ -60,6 +60,7 @@ private static class MountInfo
 
     private final Map<IComputerAccess, MountInfo> m_computers;
 
+    @Nonnull
     private ItemStack m_diskStack;
     private final IItemHandlerModifiable m_itemHandler = new InvWrapper( this );
     private IMount m_diskMount;
@@ -73,7 +74,7 @@ public TileDiskDrive()
     {
         m_computers = new HashMap<IComputerAccess, MountInfo>();
 
-        m_diskStack = null;
+        m_diskStack = ItemStack.EMPTY;
         m_diskMount = null;
         
         m_recordQueued = false;
@@ -100,15 +101,15 @@ public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, flo
         if( player.isSneaking() )
         {
             // Try to put a disk into the drive
-            if( !worldObj.isRemote )
+            if( !getWorld().isRemote )
             {
                 ItemStack disk = player.getHeldItem( EnumHand.MAIN_HAND );
-                if( disk != null && getStackInSlot(0) == null )
+                if( !disk.isEmpty() && getStackInSlot(0).isEmpty() )
                 {
                     if( ComputerCraft.getMedia( disk ) != null )
                     {
                         setInventorySlotContents( 0, disk );
-                        player.setHeldItem( EnumHand.MAIN_HAND, null );
+                        player.setHeldItem( EnumHand.MAIN_HAND, ItemStack.EMPTY );
                         return true;
                     }
                 }
@@ -117,7 +118,7 @@ public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, flo
         else
         {
             // Open the GUI
-            if( !worldObj.isRemote )
+            if( !getWorld().isRemote )
             {
                 ComputerCraft.openDiskDriveGUI( player, this );
             }
@@ -150,7 +151,7 @@ public void readFromNBT(NBTTagCompound nbttagcompound)
         if( nbttagcompound.hasKey( "item" ) )
         {
             NBTTagCompound item = nbttagcompound.getCompoundTag( "item" );
-            m_diskStack = ItemStack.loadItemStackFromNBT( item );
+            m_diskStack = new ItemStack( item );
             m_diskMount = null;
         }
     }
@@ -160,7 +161,7 @@ public void readFromNBT(NBTTagCompound nbttagcompound)
     public NBTTagCompound writeToNBT(NBTTagCompound nbttagcompound)
     {
         nbttagcompound = super.writeToNBT(nbttagcompound);
-        if( m_diskStack != null )
+        if( !m_diskStack.isEmpty() )
         {
             NBTTagCompound item = new NBTTagCompound();
             m_diskStack.writeToNBT( item );
@@ -221,41 +222,50 @@ public int getSizeInventory()
         return 1;
     }
 
+    @Override
+    public boolean isEmpty()
+    {
+        return m_diskStack.isEmpty();
+    }
+
+    @Nonnull
     @Override
     public ItemStack getStackInSlot(int i)
     {
         return m_diskStack;
     }
 
+    @Nonnull
     @Override
     public ItemStack removeStackFromSlot(int i)
     {
         ItemStack result = m_diskStack;
-        m_diskStack = null;
+        m_diskStack = ItemStack.EMPTY;
         m_diskMount = null;
         
         return result;
     }
     
+    @Nonnull
     @Override
     public ItemStack decrStackSize(int i, int j)
     {
-        if (m_diskStack == null)
+        if (m_diskStack.isEmpty())
         {
-            return null;
+            return ItemStack.EMPTY;
         }
         
-        if (m_diskStack.stackSize <= j)
+        if (m_diskStack.getCount() <= j)
         {
             ItemStack disk = m_diskStack;
-            setInventorySlotContents( 0, null );
+            setInventorySlotContents( 0, ItemStack.EMPTY );
             return disk;
         }
         
         ItemStack part = m_diskStack.splitStack(j);
-        if (m_diskStack.stackSize == 0)
+        if (m_diskStack.isEmpty())
         {
-            setInventorySlotContents( 0, null );
+            setInventorySlotContents( 0, ItemStack.EMPTY );
         }
         else
         {
@@ -265,9 +275,9 @@ public ItemStack decrStackSize(int i, int j)
     }
 
     @Override
-    public void setInventorySlotContents( int i, ItemStack itemStack )
+    public void setInventorySlotContents( int i, @Nonnull ItemStack itemStack )
     {                    
-        if( worldObj.isRemote )
+        if( getWorld().isRemote )
         {
             m_diskStack = itemStack;
             m_diskMount = null;
@@ -284,7 +294,7 @@ public void setInventorySlotContents( int i, ItemStack itemStack )
             }
             
             // Unmount old disk
-            if( m_diskStack != null )
+            if( !m_diskStack.isEmpty() )
             {
                 Set<IComputerAccess> computers = m_computers.keySet();
                 for( IComputerAccess computer : computers )
@@ -310,7 +320,7 @@ public void setInventorySlotContents( int i, ItemStack itemStack )
             updateAnim();
 
             // Mount new disk
-            if( m_diskStack != null )
+            if( !m_diskStack.isEmpty() )
             {
                 Set<IComputerAccess> computers = m_computers.keySet();
                 for( IComputerAccess computer : computers )
@@ -379,7 +389,7 @@ public boolean isItemValidForSlot( int i, @Nonnull ItemStack itemstack)
     }
 
     @Override
-    public boolean isUseableByPlayer( @Nonnull EntityPlayer player )
+    public boolean isUsableByPlayer( @Nonnull EntityPlayer player )
     {
         return isUsable( player, false );
     }
@@ -389,7 +399,7 @@ public void clear()
     {
         synchronized( this )
         {
-            setInventorySlotContents( 0, null );
+            setInventorySlotContents( 0, ItemStack.EMPTY );
         }
     }
 
@@ -426,7 +436,7 @@ public ItemStack getDiskStack()
         }
     }
 
-    public void setDiskStack( ItemStack stack )
+    public void setDiskStack( @Nonnull ItemStack stack )
     {
         synchronized( this )
         {
@@ -507,7 +517,7 @@ public void ejectDisk()
     
     private synchronized void mountDisk( IComputerAccess computer )
     {
-        if( m_diskStack != null )
+        if( !m_diskStack.isEmpty() )
         {
             MountInfo info = m_computers.get( computer );
             IMedia contents = getDiskMedia();
@@ -515,7 +525,7 @@ private synchronized void mountDisk( IComputerAccess computer )
             {
                 if( m_diskMount == null )
                 {
-                    m_diskMount = contents.createDataMount( m_diskStack, worldObj );
+                    m_diskMount = contents.createDataMount( m_diskStack, getWorld() );
                 }
                 if( m_diskMount != null )
                 {
@@ -551,7 +561,7 @@ private synchronized void mountDisk( IComputerAccess computer )
 
     private synchronized void unmountDisk( IComputerAccess computer )
     {
-        if( m_diskStack != null )
+        if( !m_diskStack.isEmpty() )
         {
             MountInfo info = m_computers.get( computer );
             assert( info != null );
@@ -566,7 +576,7 @@ private synchronized void unmountDisk( IComputerAccess computer )
 
     private synchronized void updateAnim()
     {            
-        if( m_diskStack != null )
+        if( !m_diskStack.isEmpty() )
         {
             IMedia contents = getDiskMedia();
             if( contents != null ) {
@@ -583,16 +593,16 @@ private synchronized void updateAnim()
         
     private synchronized void ejectContents( boolean destroyed )
     {
-        if( worldObj.isRemote )
+        if( getWorld().isRemote )
         {
             return;
         }
         
-        if( m_diskStack != null )
+        if( !m_diskStack.isEmpty() )
         {
             // Remove the disks from the inventory
             ItemStack disks = m_diskStack;
-            setInventorySlotContents( 0, null );
+            setInventorySlotContents( 0, ItemStack.EMPTY );
 
             // Spawn the item in the world
             int xOff = 0;
@@ -608,15 +618,15 @@ private synchronized void ejectContents( boolean destroyed )
             double x = (double)pos.getX() + 0.5 + ((double)xOff * 0.5);
             double y = (double)pos.getY() + 0.75;
             double z = (double)pos.getZ() + 0.5 + ((double)zOff * 0.5);
-            EntityItem entityitem = new EntityItem( worldObj, x, y, z, disks );
+            EntityItem entityitem = new EntityItem( getWorld(), x, y, z, disks );
             entityitem.motionX = (double)xOff * 0.15;
             entityitem.motionY = 0.0;
             entityitem.motionZ = (double)zOff * 0.15;
             
-            worldObj.spawnEntityInWorld(entityitem);
+            getWorld().spawnEntity(entityitem);
             if( !destroyed )
             {
-                worldObj.playBroadcastSound(1000, getPos(), 0);
+                getWorld().playBroadcastSound(1000, getPos(), 0);
             }
         }
     }
@@ -627,11 +637,11 @@ public final void readDescription( @Nonnull NBTTagCompound nbttagcompound )
         super.readDescription( nbttagcompound );
         if( nbttagcompound.hasKey( "item" ) )
         {
-            m_diskStack = ItemStack.loadItemStackFromNBT( nbttagcompound.getCompoundTag( "item" ) );
+            m_diskStack = new ItemStack( nbttagcompound.getCompoundTag( "item" ) );
         }
         else
         {
-            m_diskStack = null;
+            m_diskStack = ItemStack.EMPTY;
         }
         updateBlock();
     }
@@ -640,7 +650,7 @@ public final void readDescription( @Nonnull NBTTagCompound nbttagcompound )
     public void writeDescription( @Nonnull NBTTagCompound nbttagcompound )
     {
         super.writeDescription( nbttagcompound );
-        if( m_diskStack != null )
+        if( !m_diskStack.isEmpty() )
         {
             NBTTagCompound item = new NBTTagCompound();
             m_diskStack.writeToNBT( item );
@@ -681,17 +691,17 @@ private void playRecord()
         SoundEvent record = (contents != null) ? contents.getAudio( m_diskStack ) : null;
         if( record != null )
         {
-            ComputerCraft.playRecord( record, contents.getAudioTitle( m_diskStack ), worldObj, getPos() );
+            ComputerCraft.playRecord( record, contents.getAudioTitle( m_diskStack ), getWorld(), getPos() );
         }
         else
         {
-            ComputerCraft.playRecord( null, null, worldObj, getPos() );
+            ComputerCraft.playRecord( null, null, getWorld(), getPos() );
         }
     }
 
     private void stopRecord()
     {
-        ComputerCraft.playRecord( null, null, worldObj, getPos() );
+        ComputerCraft.playRecord( null, null, getWorld(), getPos() );
     }
 
     @Override
@@ -700,7 +710,7 @@ public boolean hasCapability( @Nonnull Capability<?> capability, @Nullable EnumF
         return capability == ITEM_HANDLER_CAPABILITY ||  super.hasCapability( capability, facing );
     }
 
-    @Nonnull
+    @Nullable
     @Override
     public <T> T getCapability( @Nonnull Capability<T> capability, @Nullable EnumFacing facing )
     {

src/main/java/dan200/computercraft/shared/peripheral/modem/TileCable.java

@@ -338,7 +338,7 @@ public ItemStack getPickedItem()
     public void onNeighbourChange()
     {
         EnumFacing dir = getDirection();
-        if( !worldObj.isSideSolid(
+        if( !getWorld().isSideSolid(
             getPos().offset( dir ),
             dir.getOpposite()
         ) )
@@ -348,14 +348,14 @@ public void onNeighbourChange()
                 case WiredModem:
                 {
                     // Drop everything and remove block
-                    ((BlockGeneric)getBlockType()).dropAllItems( worldObj, getPos(), false );
-                    worldObj.setBlockToAir( getPos() );
+                    ((BlockGeneric)getBlockType()).dropAllItems( getWorld(), getPos(), false );
+                    getWorld().setBlockToAir( getPos() );
                     break;
                 }
                 case WiredModemWithCable:
                 {
                     // Drop the modem and convert to cable
-                    ((BlockGeneric)getBlockType()).dropItem( worldObj, getPos(), PeripheralItemFactory.create( PeripheralType.WiredModem, getLabel(), 1 ) );
+                    ((BlockGeneric)getBlockType()).dropItem( getWorld(), getPos(), PeripheralItemFactory.create( PeripheralType.WiredModem, getLabel(), 1 ) );
                     setLabel( null );
                     setBlockState( getBlockState().withProperty( BlockCable.Properties.MODEM, BlockCableModemVariant.None ) );
                     break;
@@ -378,27 +378,28 @@ public AxisAlignedBB getCableBounds()
         double yMax = 0.625;
         double zMax = 0.625;
         BlockPos pos = getPos();
-        if( BlockCable.isCable( worldObj, pos.west() ) )
+        World world = getWorld();
+        if( BlockCable.isCable( world, pos.west() ) )
         {
             xMin = 0.0;
         }
-        if( BlockCable.isCable( worldObj, pos.east() ) )
+        if( BlockCable.isCable( world, pos.east() ) )
         {
             xMax = 1.0;
         }
-        if( BlockCable.isCable( worldObj, pos.down() ) )
+        if( BlockCable.isCable( world, pos.down() ) )
         {
             yMin = 0.0;
         }
-        if( BlockCable.isCable( worldObj, pos.up() ) )
+        if( BlockCable.isCable( world, pos.up() ) )
         {
             yMax = 1.0;
         }
-        if( BlockCable.isCable( worldObj, pos.north() )  )
+        if( BlockCable.isCable( world, pos.north() )  )
         {
             zMin = 0.0;
         }
-        if( BlockCable.isCable( worldObj, pos.south() ) )
+        if( BlockCable.isCable( world, pos.south() ) )
         {
             zMax = 1.0;
         }
@@ -444,7 +445,7 @@ public void getCollisionBounds( @Nonnull List<AxisAlignedBB> bounds )
             BlockPos pos = getPos();
             for (EnumFacing facing : EnumFacing.VALUES)
             {
-                if( BlockCable.isCable( worldObj, pos.offset( facing ) ) )
+                if( BlockCable.isCable( getWorld(), pos.offset( facing ) ) )
                 {
                     bounds.add( BOXES[ facing.ordinal() ] );
                 }
@@ -457,7 +458,7 @@ public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, flo
     {
         if( getPeripheralType() == PeripheralType.WiredModemWithCable && !player.isSneaking() )
         {
-            if( !worldObj.isRemote )
+            if( !getWorld().isRemote )
             {
                 // On server, we interacted if a peripheral was found
                 String oldPeriphName = getConnectedPeripheralName();
@@ -468,13 +469,13 @@ public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, flo
                 {
                     if( oldPeriphName != null )
                     {
-                        player.addChatMessage(
+                        player.sendMessage(
                             new TextComponentTranslation( "gui.computercraft:wired_modem.peripheral_disconnected", oldPeriphName )
                         );
                     }
                     if( periphName != null )
                     {
-                        player.addChatMessage(
+                        player.sendMessage(
                             new TextComponentTranslation( "gui.computercraft:wired_modem.peripheral_connected", periphName )
                         );
                     }
@@ -548,7 +549,7 @@ public IPeripheral getPeripheral( EnumFacing side )
     public void update()
     {
         super.update();
-        if( !worldObj.isRemote )
+        if( !getWorld().isRemote )
         {        
             synchronized( m_peripheralsByName )
             {
@@ -678,7 +679,7 @@ private Object[] callMethodRemote( String remoteName, ILuaContext context, Strin
 
     public void networkChanged()
     {
-        if( !worldObj.isRemote )
+        if( !getWorld().isRemote )
         {
             if( !m_destroyed )
             {
@@ -699,9 +700,9 @@ public void visit( TileCable modem, int distance )
                 for( EnumFacing dir : EnumFacing.values() )
                 {
                     BlockPos offset = getPos().offset( dir );
-                    if( offset.getY() >= 0 && offset.getY() < worldObj.getHeight() && BlockCable.isCable( worldObj, offset ) )
+                    if( offset.getY() >= 0 && offset.getY() < getWorld().getHeight() && BlockCable.isCable( getWorld(), offset ) )
                     {
-                        TileEntity tile = worldObj.getTileEntity( offset );
+                        TileEntity tile = getWorld().getTileEntity( offset );
                         if( tile != null && tile instanceof TileCable )
                         {
                             TileCable modem = (TileCable)tile;
@@ -954,7 +955,7 @@ public String getConnectedPeripheralName()
             if( m_attachedPeripheralID < 0 )
             {
                 m_attachedPeripheralID = IDAssigner.getNextIDFromFile(new File(
-                    ComputerCraft.getWorldDir(worldObj),
+                    ComputerCraft.getWorldDir(getWorld()),
                     "computer/lastid_" + type + ".txt"
                 ));
             }
@@ -971,7 +972,7 @@ private IPeripheral getConnectedPeripheral()
             {
                 EnumFacing facing = getDirection();
                 BlockPos neighbour = getPos().offset( facing );
-                return PeripheralUtil.getPeripheral( worldObj, neighbour, facing.getOpposite() );
+                return PeripheralUtil.getPeripheral( getWorld(), neighbour, facing.getOpposite() );
             }
         }
         return null;
@@ -1034,7 +1035,7 @@ private void searchNetwork( ICableVisitor visitor )
     {
         int searchID = ++s_nextUniqueSearchID;
         Queue<SearchLoc> queue = new LinkedList<SearchLoc>();
-        enqueue( queue, worldObj, getPos(), 1 );
+        enqueue( queue, getWorld(), getPos(), 1 );
         
         int visited = 0;
         while( queue.peek() != null )

src/main/java/dan200/computercraft/shared/peripheral/modem/TileModemBase.java

@@ -56,14 +56,14 @@ public boolean isSolidOnSide( int side )
     public void onNeighbourChange()
     {
         EnumFacing dir = getDirection();
-        if( !worldObj.isSideSolid(
+        if( !getWorld().isSideSolid(
             getPos().offset( dir ),
             dir.getOpposite()
         ) )
         {
             // Drop everything and remove block
-            ((BlockGeneric)getBlockType()).dropAllItems( worldObj, getPos(), false );
-            worldObj.setBlockToAir( getPos() );
+            ((BlockGeneric)getBlockType()).dropAllItems( getWorld(), getPos(), false );
+            getWorld().setBlockToAir( getPos() );
         }
     }
 
@@ -79,7 +79,7 @@ public AxisAlignedBB getBounds()
     public void update()
     {
         super.update();
-        if( !worldObj.isRemote && m_modem.pollChanged() )
+        if( !getWorld().isRemote && m_modem.pollChanged() )
         {
             updateAnim();
         }

src/main/java/dan200/computercraft/shared/peripheral/monitor/TileMonitor.java

@@ -86,7 +86,7 @@ public void destroy()
         if( !m_destroyed )
         {
             m_destroyed = true;
-            if( !worldObj.isRemote )
+            if( !getWorld().isRemote )
             {
                 contractNeighbours();
             }
@@ -103,7 +103,7 @@ public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, flo
     {
         if( !player.isSneaking() && getFront() == side )
         {
-            if( !worldObj.isRemote )
+            if( !getWorld().isRemote )
             {
                 monitorTouched( hitX, hitY, hitZ );
             }
@@ -141,7 +141,7 @@ public void update()
     {
         super.update();
 
-        if( !worldObj.isRemote )
+        if( !getWorld().isRemote )
         {
             if( m_sizeChangedQueued )
             {
@@ -264,7 +264,7 @@ public ITerminal getTerminal()
 
     private ITerminal getLocalTerminal()
     {
-        if( !worldObj.isRemote )
+        if( !getWorld().isRemote )
         {
             if( m_serverTerminal == null )
             {
@@ -422,11 +422,12 @@ private TileMonitor getSimilarMonitorAt( BlockPos pos )
         }
 
         int y = pos.getY();
-        if( worldObj != null && y >= 0 && y < worldObj.getHeight() )
+        World world = getWorld();
+        if( world != null && y >= 0 && y < world.getHeight() )
         {
-            if( worldObj.isBlockLoaded( pos ) )
+            if( world.isBlockLoaded( pos ) )
             {
-                TileEntity tile = worldObj.getTileEntity( pos );
+                TileEntity tile = world.getTileEntity( pos );
                 if( tile != null && tile instanceof TileMonitor )
                 {
                     TileMonitor monitor = (TileMonitor)tile;

src/main/java/dan200/computercraft/shared/peripheral/printer/ContainerPrinter.java

@@ -100,13 +100,14 @@ public void updateProgressBar(int i, int j)
     @Override
     public boolean canInteractWith( @Nonnull EntityPlayer player )
     {
-        return m_printer.isUseableByPlayer( player );
+        return m_printer.isUsableByPlayer( player );
     }
 
+    @Nonnull
     @Override
     public ItemStack transferStackInSlot(EntityPlayer par1EntityPlayer, int i)
     {
-        ItemStack itemstack = null;
+        ItemStack itemstack = ItemStack.EMPTY;
         Slot slot = inventorySlots.get(i);
         if( slot != null && slot.getHasStack() )
         {
@@ -117,7 +118,7 @@ public ItemStack transferStackInSlot(EntityPlayer par1EntityPlayer, int i)
                 // Transfer from printer to inventory
                 if(!mergeItemStack(itemstack1, 13, 49, true))
                 {
-                    return null;
+                    return ItemStack.EMPTY;
                 }
             }
             else 
@@ -127,34 +128,34 @@ public ItemStack transferStackInSlot(EntityPlayer par1EntityPlayer, int i)
                 {
                     if( !mergeItemStack(itemstack1, 0, 1, false) )
                     {
-                        return null;
+                        return ItemStack.EMPTY;
                     }
                 }
                 else //if is paper
                 {
                     if( !mergeItemStack(itemstack1, 1, 13, false) )
                     {
-                        return null;
+                        return ItemStack.EMPTY;
                     }
                 }
             }
             
-            if(itemstack1.stackSize == 0)
+            if(itemstack1.isEmpty())
             {
-                slot.putStack(null);
+                slot.putStack(ItemStack.EMPTY);
             }
             else
             {
                 slot.onSlotChanged();
             }
             
-            if(itemstack1.stackSize != itemstack.stackSize)
+            if(itemstack1.getCount() != itemstack.getCount())
             {
-                slot.onPickupFromSlot(par1EntityPlayer, itemstack1);
+                slot.onTake(par1EntityPlayer, itemstack1);
             }
             else
             {
-                return null;
+                return ItemStack.EMPTY;
             }
         }
         return itemstack;

src/main/java/dan200/computercraft/shared/peripheral/printer/TilePrinter.java

@@ -24,6 +24,7 @@
 import net.minecraft.nbt.NBTTagCompound;
 import net.minecraft.nbt.NBTTagList;
 import net.minecraft.util.EnumFacing;
+import net.minecraft.util.NonNullList;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.text.ITextComponent;
 import net.minecraft.util.text.TextComponentString;
@@ -51,7 +52,7 @@ public class TilePrinter extends TilePeripheralBase
 
     // Members
 
-    private final ItemStack[] m_inventory;
+    private final NonNullList<ItemStack> m_inventory;
     private final IItemHandlerModifiable m_itemHandlerAll = new InvWrapper( this );
     private IItemHandlerModifiable[] m_itemHandlerSides;
     
@@ -61,7 +62,7 @@ public class TilePrinter extends TilePeripheralBase
 
     public TilePrinter()
     {
-        m_inventory = new ItemStack[13];
+        m_inventory = NonNullList.withSize( 13, ItemStack.EMPTY );
         m_page = new Terminal( ItemPrintout.LINE_MAX_LENGTH, ItemPrintout.LINES_PER_PAGE );
         m_pageTitle = "";
         m_printing = false;
@@ -78,7 +79,7 @@ public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, flo
     {
         if( !player.isSneaking() )
         {
-            if( !worldObj.isRemote )
+            if( !getWorld().isRemote )
             {
                 ComputerCraft.openPrinterGUI( player, this );
             }
@@ -108,9 +109,9 @@ public void readFromNBT(NBTTagCompound nbttagcompound)
             {
                 NBTTagCompound itemTag = nbttaglist.getCompoundTagAt( i );
                 int j = itemTag.getByte("Slot") & 0xff;
-                if (j >= 0 && j < m_inventory.length)
+                if (j >= 0 && j < m_inventory.size())
                 {
-                    m_inventory[j] = ItemStack.loadItemStackFromNBT(itemTag);
+                    m_inventory.set( j, new ItemStack( itemTag ) );
                 }
             }
         }
@@ -134,13 +135,13 @@ public NBTTagCompound writeToNBT(NBTTagCompound nbttagcompound)
         synchronized( m_inventory )
         {
             NBTTagList nbttaglist = new NBTTagList();
-            for(int i=0; i<m_inventory.length; ++i)
+            for(int i=0; i<m_inventory.size(); ++i)
             {
-                if (m_inventory[i] != null)
+                if( !m_inventory.get( i ).isEmpty() )
                 {
                     NBTTagCompound itemtag = new NBTTagCompound();
                     itemtag.setByte("Slot", (byte)i);
-                    m_inventory[i].writeToNBT(itemtag);
+                    m_inventory.get( i ).writeToNBT( itemtag );
                     nbttaglist.appendTag(itemtag);
                 }
             }
@@ -173,53 +174,66 @@ public boolean isPrinting()
     @Override    
     public int getSizeInventory()
     {
-        return m_inventory.length;
+        return m_inventory.size();
     }
 
+    @Override
+    public boolean isEmpty()
+    {
+        for( ItemStack stack : m_inventory )
+        {
+            if( !stack.isEmpty() ) return false;
+        }
+        return true;
+    }
+
+    @Nonnull
     @Override    
     public ItemStack getStackInSlot(int i)
     {
         synchronized( m_inventory )
         {
-            return m_inventory[i];
+            return m_inventory.get( i );
         }
     }
 
+    @Nonnull
     @Override    
     public ItemStack removeStackFromSlot(int i)
     {
         synchronized( m_inventory )
         {
-            ItemStack result = m_inventory[i];
-            m_inventory[i] = null;
+            ItemStack result = m_inventory.get( i );
+            m_inventory.set( i, ItemStack.EMPTY );
             updateAnim();
             return result;
         }
     }
     
+    @Nonnull
     @Override    
     public ItemStack decrStackSize(int i, int j)
     {
         synchronized( m_inventory )
         {
-            if( m_inventory[i] == null )
+            if( m_inventory.get( i ).isEmpty() )
             {
-                return null;
+                return ItemStack.EMPTY;
             }
             
-            if( m_inventory[i].stackSize <= j )
+            if( m_inventory.get( i ).getCount() <= j )
             {
-                ItemStack itemstack = m_inventory[i];
-                m_inventory[i] = null;
+                ItemStack itemstack = m_inventory.get( i );
+                m_inventory.set( i, ItemStack.EMPTY );
                 markDirty();
                 updateAnim();
                 return itemstack;
             }
             
-            ItemStack part = m_inventory[i].splitStack(j);
-            if( m_inventory[i].stackSize == 0 )
+            ItemStack part = m_inventory.get( i ).splitStack(j);
+            if( m_inventory.get( i ).isEmpty() )
             {
-                m_inventory[i] = null;
+                m_inventory.set( i, ItemStack.EMPTY );
                 updateAnim();
             }
             markDirty();
@@ -228,11 +242,11 @@ public ItemStack decrStackSize(int i, int j)
     }
 
     @Override    
-    public void setInventorySlotContents( int i, ItemStack stack )
+    public void setInventorySlotContents( int i, @Nonnull ItemStack stack )
     {                    
         synchronized( m_inventory )
         {
-            m_inventory[i] = stack;
+            m_inventory.set( i, stack );
             markDirty();
             updateAnim();
         }
@@ -243,9 +257,9 @@ public void clear()
     {
         synchronized( m_inventory )
         {
-            for( int i=0; i<m_inventory.length; ++i )
+            for( int i=0; i<m_inventory.size(); ++i )
             {
-                m_inventory[i] = null;
+                m_inventory.set( i, ItemStack.EMPTY );
             }
             markDirty();
             updateAnim();
@@ -310,7 +324,7 @@ public boolean isItemValidForSlot( int slot, @Nonnull ItemStack itemstack )
     }
 
     @Override
-    public boolean isUseableByPlayer( @Nonnull EntityPlayer player )
+    public boolean isUsableByPlayer( @Nonnull EntityPlayer player )
     {
         return isUsable( player, false );
     }
@@ -410,10 +424,10 @@ public int getInkLevel()
     {
         synchronized( m_inventory )
         {
-            ItemStack inkStack = m_inventory[0];
-            if( inkStack != null && isInk(inkStack) )
+            ItemStack inkStack = m_inventory.get( 0 );
+            if( !inkStack.isEmpty() && isInk(inkStack) )
             {
-                return inkStack.stackSize;
+                return inkStack.getCount();
             }
         }
         return 0;
@@ -426,10 +440,10 @@ public int getPaperLevel()
         {
             for( int i=1; i<7; ++i )
             {
-                ItemStack paperStack = m_inventory[i];
-                if( paperStack != null && isPaper(paperStack) )
+                ItemStack paperStack = m_inventory.get( i );
+                if( !paperStack.isEmpty() && isPaper(paperStack) )
                 {
-                    count += paperStack.stackSize;
+                    count += paperStack.getCount();
                 }
             }
         }
@@ -444,12 +458,12 @@ public void setPageTitle( String title )
         }
     }
     
-    private boolean isInk( ItemStack stack )
+    private boolean isInk( @Nonnull ItemStack stack )
     {
         return (stack.getItem() == Items.DYE);
     }
 
-    private boolean isPaper( ItemStack stack )
+    private boolean isPaper( @Nonnull ItemStack stack )
     {
         Item item = stack.getItem();
         return ( item == Items.PAPER || (item instanceof ItemPrintout && ItemPrintout.getType( stack ) == ItemPrintout.Type.Single) );
@@ -459,8 +473,8 @@ private boolean canInputPage()
     {
         synchronized( m_inventory )
         {
-            ItemStack inkStack = m_inventory[ 0 ];
-            return inkStack != null && isInk( inkStack ) && getPaperLevel() > 0;
+            ItemStack inkStack = m_inventory.get( 0 );
+            return !inkStack.isEmpty() && isInk( inkStack ) && getPaperLevel() > 0;
         }
     }
     
@@ -468,29 +482,29 @@ private boolean inputPage()
     {        
         synchronized( m_inventory )
         {
-            ItemStack inkStack = m_inventory[0];
-            if( inkStack == null || !isInk(inkStack) )
+            ItemStack inkStack = m_inventory.get( 0 );
+            if( inkStack.isEmpty() || !isInk(inkStack) )
             {
                 return false;
             }
             
             for( int i=1; i<7; ++i )
             {
-                ItemStack paperStack = m_inventory[i];
-                if( paperStack != null && isPaper(paperStack) )
+                ItemStack paperStack = m_inventory.get( i );
+                if( !paperStack.isEmpty() && isPaper(paperStack) )
                 {
                     // Decrement ink
-                    inkStack.stackSize--;
-                    if( inkStack.stackSize <= 0 )
+                    inkStack.shrink( 1 );
+                    if( inkStack.isEmpty() )
                     {
-                        m_inventory[0] = null;
+                        m_inventory.set( 0, ItemStack.EMPTY );
                     }
                                         
                     // Decrement paper
-                    paperStack.stackSize--;
-                    if( paperStack.stackSize <= 0 )
+                    paperStack.shrink( 1 );
+                    if( paperStack.isEmpty() )
                     {
-                        m_inventory[i] = null;
+                        m_inventory.set( i, ItemStack.EMPTY );
                         updateAnim();
                     }
                     
@@ -545,7 +559,7 @@ private boolean outputPage()
             synchronized( m_inventory )
             {
                 ItemStack remainder = InventoryUtil.storeItems( stack, m_itemHandlerAll, 7, 6, 7 );
-                if( remainder == null )
+                if( remainder.isEmpty() )
                 {
                     m_printing = false;
                     return true;
@@ -561,22 +575,22 @@ private void ejectContents()
         {
             for( int i=0; i<13; ++i ) 
             {
-                ItemStack stack = m_inventory[i];
-                if( stack != null )
+                ItemStack stack = m_inventory.get( i );
+                if( !stack.isEmpty() )
                 {
                     // Remove the stack from the inventory
-                    setInventorySlotContents( i, null );
+                    setInventorySlotContents( i, ItemStack.EMPTY );
         
                     // Spawn the item in the world
                     BlockPos pos = getPos();
                     double x = (double)pos.getX() + 0.5;
                     double y = (double)pos.getY() + 0.75;
                     double z = (double)pos.getZ() + 0.5;
-                    EntityItem entityitem = new EntityItem( worldObj, x, y, z, stack );
-                    entityitem.motionX = worldObj.rand.nextFloat() * 0.2 - 0.1;
-                    entityitem.motionY = worldObj.rand.nextFloat() * 0.2 - 0.1;
-                    entityitem.motionZ = worldObj.rand.nextFloat() * 0.2 - 0.1;
-                    worldObj.spawnEntityInWorld(entityitem);
+                    EntityItem entityitem = new EntityItem( getWorld(), x, y, z, stack );
+                    entityitem.motionX = getWorld().rand.nextFloat() * 0.2 - 0.1;
+                    entityitem.motionY = getWorld().rand.nextFloat() * 0.2 - 0.1;
+                    entityitem.motionZ = getWorld().rand.nextFloat() * 0.2 - 0.1;
+                    getWorld().spawnEntity(entityitem);
                 }
             }
         }
@@ -589,8 +603,8 @@ private void updateAnim()
             int anim = 0;
             for( int i=1;i<7;++i )
             {
-                ItemStack stack = m_inventory[i];
-                if( stack != null && isPaper(stack) )
+                ItemStack stack = m_inventory.get( i );
+                if( !stack.isEmpty() && isPaper(stack) )
                 {
                     anim += 1;
                     break;
@@ -598,8 +612,8 @@ private void updateAnim()
             }
             for( int i=7;i<13;++i )
             {
-                ItemStack stack = m_inventory[i];
-                if( stack != null && isPaper(stack) )
+                ItemStack stack = m_inventory.get( i );
+                if( !stack.isEmpty() && isPaper(stack) )
                 {
                     anim += 2;
                     break;
@@ -615,7 +629,7 @@ public boolean hasCapability( @Nonnull Capability<?> capability, @Nullable EnumF
         return capability == ITEM_HANDLER_CAPABILITY || super.hasCapability( capability, facing );
     }
 
-    @Nonnull
+    @Nullable
     @Override
     public <T> T getCapability( @Nonnull Capability<T> capability, @Nullable EnumFacing facing )
     {

src/main/java/dan200/computercraft/shared/pocket/apis/PocketAPI.java

@@ -18,6 +18,7 @@
 import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.entity.player.InventoryPlayer;
 import net.minecraft.item.ItemStack;
+import net.minecraft.util.NonNullList;
 import net.minecraftforge.items.wrapper.PlayerMainInvWrapper;
 
 import javax.annotation.Nonnull;
@@ -99,12 +100,12 @@ public Object[] execute() throws LuaException
                         if( previousUpgrade != null )
                         {
                             ItemStack stack = previousUpgrade.getCraftingItem();
-                            if( stack != null )
+                            if( !stack.isEmpty() )
                             {
                                 stack = InventoryUtil.storeItems( stack, new PlayerMainInvWrapper( inventory ), inventory.currentItem );
-                                if( stack != null )
+                                if( !stack.isEmpty() )
                                 {
-                                    WorldUtil.dropItemStack( stack, player.worldObj, player.posX, player.posY, player.posZ );
+                                    WorldUtil.dropItemStack( stack, player.getEntityWorld(), player.posX, player.posY, player.posZ );
                                 }
                             }
                         }
@@ -138,12 +139,12 @@ public Object[] execute() throws LuaException
                         m_computer.setUpgrade( null );
 
                         ItemStack stack = previousUpgrade.getCraftingItem();
-                        if( stack != null )
+                        if( !stack.isEmpty() )
                         {
                             stack = InventoryUtil.storeItems( stack, new PlayerMainInvWrapper( inventory ), inventory.currentItem );
-                            if( stack != null )
+                            if( stack.isEmpty() )
                             {
-                                WorldUtil.dropItemStack( stack, player.worldObj, player.posX, player.posY, player.posZ );
+                                WorldUtil.dropItemStack( stack, player.getEntityWorld(), player.posX, player.posY, player.posZ );
                             }
                         }
 
@@ -155,12 +156,12 @@ public Object[] execute() throws LuaException
         }
     }
 
-    private static IPocketUpgrade findUpgrade( ItemStack[] inv, int start, IPocketUpgrade previous )
+    private static IPocketUpgrade findUpgrade( NonNullList<ItemStack> inv, int start, IPocketUpgrade previous )
     {
-        for (int i = 0; i < inv.length; i++)
+        for( int i = 0; i < inv.size(); i++ )
         {
-            ItemStack invStack = inv[ (i + start) % inv.length ];
-            if( invStack != null )
+            ItemStack invStack = inv.get( (i + start) % inv.size() );
+            if( !invStack.isEmpty() )
             {
                 IPocketUpgrade newUpgrade = ComputerCraft.getPocketUpgrade( invStack );
 
@@ -168,8 +169,8 @@ private static IPocketUpgrade findUpgrade( ItemStack[] inv, int start, IPocketUp
                 {
                     // Consume an item from this stack and exit the loop
                     invStack = invStack.copy();
-                    invStack.stackSize--;
-                    inv[ (i + start) % inv.length ] = invStack.stackSize <= 0 ? null : invStack;
+                    invStack.shrink( 1 );
+                    inv.set( (i + start) % inv.size(), invStack.isEmpty() ? ItemStack.EMPTY : invStack );
 
                     return newUpgrade;
                 }

src/main/java/dan200/computercraft/shared/pocket/core/PocketServerComputer.java

@@ -148,7 +148,7 @@ public void setUpgrade( IPocketUpgrade upgrade )
         }
     }
 
-    public synchronized void updateValues( Entity entity, ItemStack stack, IPocketUpgrade upgrade )
+    public synchronized void updateValues( Entity entity, @Nonnull ItemStack stack, IPocketUpgrade upgrade )
     {
         if( entity != null )
         {

src/main/java/dan200/computercraft/shared/pocket/inventory/ContainerPocketComputer.java

@@ -23,7 +23,7 @@ public ContainerPocketComputer( EntityPlayer player, EnumHand hand )
     public IComputer getComputer()
     {
         ItemStack stack = getStack();
-        if( stack != null && stack.getItem() instanceof ItemPocketComputer )
+        if( !stack.isEmpty() && stack.getItem() instanceof ItemPocketComputer )
         {
             return ((ItemPocketComputer) stack.getItem()).getServerComputer( stack );
         }

src/main/java/dan200/computercraft/shared/pocket/items/ItemPocketComputer.java

@@ -27,10 +27,7 @@
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.nbt.NBTTagCompound;
-import net.minecraft.util.ActionResult;
-import net.minecraft.util.EnumActionResult;
-import net.minecraft.util.EnumHand;
-import net.minecraft.util.SoundEvent;
+import net.minecraft.util.*;
 import net.minecraft.world.World;
 import net.minecraftforge.common.util.Constants;
 import net.minecraftforge.fml.relauncher.Side;
@@ -89,16 +86,16 @@ public ItemStack create( int id, String label, int colour, ComputerFamily family
     }
 
     @Override
-    public void getSubItems( @Nonnull Item itemID, CreativeTabs tabs, List<ItemStack> list )
+    public void getSubItems( @Nonnull Item itemID, CreativeTabs tabs, NonNullList<ItemStack> list )
     {
         getSubItems( list, ComputerFamily.Normal );
         getSubItems( list, ComputerFamily.Advanced );
     }
 
-    private void getSubItems( List<ItemStack> list, ComputerFamily family )
+    private void getSubItems( NonNullList<ItemStack> list, ComputerFamily family )
     {
         list.add( PocketComputerItemFactory.create( -1, null, -1, family, null ) );
-        for (IPocketUpgrade upgrade : ComputerCraft.getVanillaPocketUpgrades())
+        for( IPocketUpgrade upgrade : ComputerCraft.getVanillaPocketUpgrades() )
         {
             list.add( PocketComputerItemFactory.create( -1, null, -1, family, upgrade ) );
         }
@@ -163,8 +160,9 @@ public void onUpdate( ItemStack stack, World world, Entity entity, int slotNum,
 
     @Nonnull
     @Override
-    public ActionResult<ItemStack> onItemRightClick( @Nonnull ItemStack stack, World world, EntityPlayer player, EnumHand hand )
+    public ActionResult<ItemStack> onItemRightClick( World world, EntityPlayer player, @Nonnull EnumHand hand )
     {
+        ItemStack stack = player.getHeldItem( hand );
         if( !world.isRemote )
         {
             PocketServerComputer computer = createServerComputer( world, player.inventory, player, stack );
@@ -189,7 +187,7 @@ public ActionResult<ItemStack> onItemRightClick( @Nonnull ItemStack stack, World
 
     @Nonnull
     @Override
-    public String getUnlocalizedName( ItemStack stack )
+    public String getUnlocalizedName( @Nonnull ItemStack stack )
     {
         switch( getFamily( stack ) )
         {
@@ -225,7 +223,7 @@ public String getItemStackDisplayName( @Nonnull ItemStack stack )
     }
 
     @Override
-    public void addInformation( ItemStack stack, EntityPlayer player, List<String> list, boolean debug )
+    public void addInformation( @Nonnull ItemStack stack, EntityPlayer player, List<String> list, boolean debug )
     {
         if( debug )
         {
@@ -237,7 +235,7 @@ public void addInformation( ItemStack stack, EntityPlayer player, List<String> l
         }
     }
 
-    private PocketServerComputer createServerComputer( final World world, IInventory inventory, Entity entity, ItemStack stack )
+    private PocketServerComputer createServerComputer( final World world, IInventory inventory, Entity entity, @Nonnull ItemStack stack )
     {
         if( world.isRemote )
         {
@@ -287,7 +285,7 @@ private PocketServerComputer createServerComputer( final World world, IInventory
         return computer;
     }
 
-    public ServerComputer getServerComputer( ItemStack stack )
+    public ServerComputer getServerComputer( @Nonnull ItemStack stack )
     {
         int instanceID = getInstanceID( stack );
         if( instanceID >= 0 )
@@ -297,7 +295,7 @@ public ServerComputer getServerComputer( ItemStack stack )
         return null;
     }
 
-    public ClientComputer createClientComputer( ItemStack stack )
+    public ClientComputer createClientComputer( @Nonnull ItemStack stack )
     {
         int instanceID = getInstanceID( stack );
         if( instanceID >= 0 )
@@ -311,7 +309,7 @@ public ClientComputer createClientComputer( ItemStack stack )
         return null;
     }
 
-    private ClientComputer getClientComputer( ItemStack stack )
+    private ClientComputer getClientComputer( @Nonnull ItemStack stack )
     {
         int instanceID = getInstanceID( stack );
         if( instanceID >= 0 )
@@ -324,7 +322,7 @@ private ClientComputer getClientComputer( ItemStack stack )
     // IComputerItem implementation
 
     @Override
-    public int getComputerID( ItemStack stack )
+    public int getComputerID( @Nonnull ItemStack stack )
     {
         NBTTagCompound compound = stack.getTagCompound();
         if( compound != null && compound.hasKey( "computerID" ) )
@@ -334,7 +332,7 @@ public int getComputerID( ItemStack stack )
         return -1;
     }
 
-    private void setComputerID( ItemStack stack, int computerID )
+    private void setComputerID( @Nonnull ItemStack stack, int computerID )
     {
         if( !stack.hasTagCompound() )
         {
@@ -354,7 +352,7 @@ public String getLabel( @Nonnull ItemStack stack )
     }
 
     @Override
-    public ComputerFamily getFamily( ItemStack stack )
+    public ComputerFamily getFamily( @Nonnull ItemStack stack )
     {
         int damage = stack.getItemDamage();
         switch( damage )
@@ -410,7 +408,7 @@ public IMount createDataMount( @Nonnull ItemStack stack, @Nonnull World world )
         return null;
     }
 
-    private int getInstanceID( ItemStack stack )
+    private int getInstanceID( @Nonnull ItemStack stack )
     {
         NBTTagCompound compound = stack.getTagCompound();
         if( compound != null && compound.hasKey( "instanceID" ) )
@@ -420,7 +418,7 @@ private int getInstanceID( ItemStack stack )
         return -1;
     }
 
-    private void setInstanceID( ItemStack stack, int instanceID )
+    private void setInstanceID( @Nonnull ItemStack stack, int instanceID )
     {
         if( !stack.hasTagCompound() )
         {
@@ -429,7 +427,7 @@ private void setInstanceID( ItemStack stack, int instanceID )
         stack.getTagCompound().setInteger( "instanceID", instanceID );
     }
 
-    private int getSessionID( ItemStack stack )
+    private int getSessionID( @Nonnull ItemStack stack )
     {
         NBTTagCompound compound = stack.getTagCompound();
         if( compound != null && compound.hasKey( "sessionID" ) )
@@ -439,7 +437,7 @@ private int getSessionID( ItemStack stack )
         return -1;
     }
 
-    private void setSessionID( ItemStack stack, int sessionID )
+    private void setSessionID( @Nonnull ItemStack stack, int sessionID )
     {
         if( !stack.hasTagCompound() )
         {
@@ -449,7 +447,7 @@ private void setSessionID( ItemStack stack, int sessionID )
     }
 
     @SideOnly(Side.CLIENT)
-    public ComputerState getState( ItemStack stack )
+    public ComputerState getState( @Nonnull ItemStack stack )
     {
         ClientComputer computer = getClientComputer( stack );
         if( computer != null && computer.isOn() )
@@ -460,7 +458,7 @@ public ComputerState getState( ItemStack stack )
     }
 
     @SideOnly(Side.CLIENT)
-    public int getLightState( ItemStack stack )
+    public int getLightState( @Nonnull ItemStack stack )
     {
         ClientComputer computer = getClientComputer( stack );
         if( computer != null && computer.isOn() )
@@ -474,7 +472,7 @@ public int getLightState( ItemStack stack )
         return -1;
     }
 
-    public IPocketUpgrade getUpgrade( ItemStack stack )
+    public IPocketUpgrade getUpgrade( @Nonnull ItemStack stack )
     {
         NBTTagCompound compound = stack.getTagCompound();
         if( compound != null )
@@ -497,7 +495,7 @@ else if( compound.hasKey( "upgrade", Constants.NBT.TAG_ANY_NUMERIC ) )
         return null;
     }
 
-    public void setUpgrade( ItemStack stack, IPocketUpgrade upgrade )
+    public void setUpgrade( @Nonnull ItemStack stack, IPocketUpgrade upgrade )
     {
         NBTTagCompound compound = stack.getTagCompound();
         if( compound == null ) stack.setTagCompound( compound = new NBTTagCompound() );
@@ -514,7 +512,7 @@ public void setUpgrade( ItemStack stack, IPocketUpgrade upgrade )
         compound.removeTag( "upgrade_info" );
     }
 
-    public NBTTagCompound getUpgradeInfo( ItemStack stack )
+    public NBTTagCompound getUpgradeInfo( @Nonnull ItemStack stack )
     {
         NBTTagCompound tag = stack.getTagCompound();
         if( tag == null )

src/main/java/dan200/computercraft/shared/pocket/items/PocketComputerItemFactory.java

@@ -11,8 +11,11 @@
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 import net.minecraft.item.ItemStack;
 
+import javax.annotation.Nonnull;
+
 public class PocketComputerItemFactory
 {
+    @Nonnull
     public static ItemStack create( int id, String label, int colour, ComputerFamily family, IPocketUpgrade upgrade )
     {
         ItemPocketComputer computer = ComputerCraft.Items.pocketComputer;
@@ -24,6 +27,6 @@ public static ItemStack create( int id, String label, int colour, ComputerFamily
                 return computer.create( id, label, colour, family, upgrade );
             }
         }
-        return null;
+        return ItemStack.EMPTY;
     }
 }

src/main/java/dan200/computercraft/shared/pocket/peripherals/PocketModem.java

@@ -41,7 +41,7 @@ public String getUnlocalisedAdjective()
             : "upgrade.computercraft:wireless_modem.adjective";
     }
 
-    @Nullable
+    @Nonnull
     @Override
     public ItemStack getCraftingItem()
     {

src/main/java/dan200/computercraft/shared/pocket/peripherals/PocketSpeaker.java

@@ -40,7 +40,7 @@ public String getUnlocalisedAdjective()
         return "upgrade.computercraft:speaker.adjective";
     }
 
-    @Nullable
+    @Nonnull
     @Override
     public ItemStack getCraftingItem()
     {

src/main/java/dan200/computercraft/shared/pocket/recipes/PocketComputerUpgradeRecipe.java

@@ -14,7 +14,9 @@
 import net.minecraft.inventory.InventoryCrafting;
 import net.minecraft.item.ItemStack;
 import net.minecraft.item.crafting.IRecipe;
+import net.minecraft.util.NonNullList;
 import net.minecraft.world.World;
+import net.minecraftforge.common.ForgeHooks;
 
 import javax.annotation.Nonnull;
 
@@ -30,6 +32,7 @@ public int getRecipeSize()
         return 2;
     }
 
+    @Nonnull
     @Override
     public ItemStack getRecipeOutput()
     {
@@ -39,14 +42,15 @@ public ItemStack getRecipeOutput()
     @Override
     public boolean matches( @Nonnull InventoryCrafting inventory, @Nonnull World world )
     {
-        return (getCraftingResult( inventory ) != null);
+        return !getCraftingResult( inventory ).isEmpty();
     }
 
+    @Nonnull
     @Override
     public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
     {
         // Scan the grid for a pocket computer
-        ItemStack computer = null;
+        ItemStack computer = ItemStack.EMPTY;
         int computerX = -1;
         int computerY = -1;
         for (int y = 0; y < inventory.getHeight(); ++y)
@@ -54,7 +58,7 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
             for (int x = 0; x < inventory.getWidth(); ++x)
             {
                 ItemStack item = inventory.getStackInRowAndColumn( x, y );
-                if( item != null && item.getItem() instanceof ItemPocketComputer )
+                if( !item.isEmpty() && item.getItem() instanceof ItemPocketComputer )
                 {
                     computer = item;
                     computerX = x;
@@ -62,21 +66,21 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
                     break;
                 }
             }
-            if( computer != null )
+            if( !computer.isEmpty() )
             {
                 break;
             }
         }
 
-        if( computer == null )
+        if( computer.isEmpty() )
         {
-            return null;
+            return ItemStack.EMPTY;
         }
 
         ItemPocketComputer itemComputer = (ItemPocketComputer)computer.getItem();
         if( itemComputer.getUpgrade( computer ) != null )
         {
-            return null;
+            return ItemStack.EMPTY;
         }
 
         // Check for upgrades around the item
@@ -93,18 +97,18 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
                 else if( x == computerX && y == computerY - 1 )
                 {
                     upgrade = ComputerCraft.getPocketUpgrade( item );
-                    if( upgrade == null ) return null;
+                    if( upgrade == null ) return ItemStack.EMPTY;
                 }
-                else if( item != null )
+                else if( !item.isEmpty() )
                 {
-                    return null;
+                    return ItemStack.EMPTY;
                 }
             }
         }
 
         if( upgrade == null )
         {
-            return null;
+            return ItemStack.EMPTY;
         }
 
         // Construct the new stack
@@ -117,13 +121,13 @@ else if( item != null )
 
     @Nonnull
     @Override
-    public ItemStack[] getRemainingItems( @Nonnull InventoryCrafting inventoryCrafting )
+    public NonNullList<ItemStack> getRemainingItems( @Nonnull InventoryCrafting inventoryCrafting )
     {
-        ItemStack[] results = new ItemStack[ inventoryCrafting.getSizeInventory() ];
-        for (int i = 0; i < results.length; ++i)
+        NonNullList<ItemStack> results = NonNullList.withSize( inventoryCrafting.getSizeInventory(), ItemStack.EMPTY );
+        for( int i = 0; i < results.size(); ++i )
         {
-            ItemStack stack = inventoryCrafting.getStackInSlot(i);
-            results[i] = net.minecraftforge.common.ForgeHooks.getContainerItem(stack);
+            ItemStack stack = inventoryCrafting.getStackInSlot( i );
+            results.set( i, ForgeHooks.getContainerItem( stack ) );
         }
         return results;
     }

src/main/java/dan200/computercraft/shared/proxy/CCTurtleProxyCommon.java

@@ -37,6 +37,7 @@
 import net.minecraft.item.crafting.CraftingManager;
 import net.minecraft.item.crafting.IRecipe;
 import net.minecraft.tileentity.TileEntity;
+import net.minecraft.util.NonNullList;
 import net.minecraft.util.ResourceLocation;
 import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.event.entity.living.LivingDropsEvent;
@@ -46,6 +47,7 @@
 import net.minecraftforge.fml.common.registry.GameRegistry;
 import net.minecraftforge.oredict.RecipeSorter;
 
+import javax.annotation.Nonnull;
 import java.util.*;
 
 public abstract class CCTurtleProxyCommon implements ICCTurtleProxy
@@ -66,7 +68,10 @@ public CCTurtleProxyCommon()
     @Override        
     public void preInit()
     {
-        EntityRegistry.registerModEntity(TurtlePlayer.class, "turtlePlayer", 0, ComputerCraft.instance, Integer.MAX_VALUE, Integer.MAX_VALUE, false);
+        EntityRegistry.registerModEntity(
+            new ResourceLocation( ComputerCraft.MOD_ID, "turtle_player" ), TurtlePlayer.class, "turtle_player",
+            0, ComputerCraft.instance, Integer.MAX_VALUE, Integer.MAX_VALUE, false
+        );
         registerItems();
     }
     
@@ -106,7 +111,7 @@ public ITurtleUpgrade getTurtleUpgrade( int legacyId )
     }
     
     @Override
-    public ITurtleUpgrade getTurtleUpgrade( ItemStack stack )
+    public ITurtleUpgrade getTurtleUpgrade( @Nonnull ItemStack stack )
     {
         for( ITurtleUpgrade upgrade : m_turtleUpgrades.values() )
         {
@@ -143,10 +148,10 @@ public static boolean isUpgradeSuitableForFamily( ComputerFamily family, ITurtle
         }
     }
     
-    private void addAllUpgradedTurtles( ComputerFamily family, List<ItemStack> list )
+    private void addAllUpgradedTurtles( ComputerFamily family, NonNullList<ItemStack> list )
     {
         ItemStack basicStack = TurtleItemFactory.create( -1, null, -1, family, null, null, 0, null );
-        if( basicStack != null )
+        if( !basicStack.isEmpty() )
         {
             list.add( basicStack );
         }
@@ -166,7 +171,7 @@ private void addUpgradedTurtle( ComputerFamily family, ITurtleUpgrade upgrade, L
         if ( isUpgradeSuitableForFamily( family, upgrade ) )
         {
             ItemStack stack = TurtleItemFactory.create( -1, null, -1, family, upgrade, null, 0, null );
-            if( stack != null )
+            if( !stack.isEmpty() )
             {
                 list.add( stack );
             }
@@ -174,7 +179,7 @@ private void addUpgradedTurtle( ComputerFamily family, ITurtleUpgrade upgrade, L
     }
     
     @Override
-    public void addAllUpgradedTurtles( List<ItemStack> list )
+    public void addAllUpgradedTurtles( NonNullList<ItemStack> list )
     {
         addAllUpgradedTurtles( ComputerFamily.Normal, list );
         addAllUpgradedTurtles( ComputerFamily.Advanced, list );
@@ -276,7 +281,7 @@ private void registerTurtleUpgradeInternal( ITurtleUpgrade upgrade )
                 }
 
                 ItemStack baseTurtle = TurtleItemFactory.create( -1, null, -1, family, null, null, 0, null );
-                if( baseTurtle != null )
+                if( !baseTurtle.isEmpty() )
                 {
                     ItemStack craftedTurtle = TurtleItemFactory.create( -1, null, -1, family, upgrade, null, 0, null );
                     ItemStack craftedTurtleFlipped = TurtleItemFactory.create( -1, null, -1, family, null, upgrade, 0, null );
@@ -405,15 +410,15 @@ public void remap( FMLMissingMappingsEvent mappings )
             if( !domain.equalsIgnoreCase( ComputerCraft.MOD_ID ) ) continue;
 
             String key = mapping.resourceLocation.getResourcePath();
-            if( key.equals( "CC-Turtle" ) )
+            if( key.equalsIgnoreCase( "CC-Turtle" ) )
             {
                 remap( mapping, ComputerCraft.Blocks.turtle );
             }
-            else if( key.equals( "CC-TurtleExpanded" ) )
+            else if( key.equalsIgnoreCase( "CC-TurtleExpanded" ) )
             {
                 remap( mapping, ComputerCraft.Blocks.turtleExpanded );
             }
-            else if( key.equals( "CC-TurtleAdvanced" ) )
+            else if( key.equalsIgnoreCase( "CC-TurtleAdvanced" ) )
             {
                 remap( mapping, ComputerCraft.Blocks.turtleAdvanced );
             }

src/main/java/dan200/computercraft/shared/proxy/ComputerCraftProxyCommon.java

@@ -85,6 +85,7 @@
 import net.minecraftforge.fml.common.registry.GameRegistry;
 import net.minecraftforge.oredict.RecipeSorter;
 
+import javax.annotation.Nonnull;
 import java.io.File;
 
 public abstract class ComputerCraftProxyCommon implements IComputerCraftProxy
@@ -126,7 +127,7 @@ public void deleteDisplayLists( int list, int range )
     public abstract Object getFixedWidthFontRenderer();
 
     @Override
-    public String getRecordInfo( ItemStack recordStack )
+    public String getRecordInfo( @Nonnull ItemStack recordStack )
     {
         Item item = recordStack.getItem();
         if (item instanceof ItemRecord)
@@ -500,27 +501,27 @@ public void remap( FMLMissingMappingsEvent mappings )
             if( !domain.equalsIgnoreCase( ComputerCraft.MOD_ID ) ) continue;
 
             String key = mapping.resourceLocation.getResourcePath();
-            if( key.equals( "CC-Computer" ) )
+            if( key.equalsIgnoreCase( "CC-Computer" ) )
             {
                 remap( mapping, ComputerCraft.Blocks.computer );
             }
-            else if( key.equals( "CC-Peripheral" ) )
+            else if( key.equalsIgnoreCase( "CC-Peripheral" ) )
             {
                 remap( mapping, ComputerCraft.Blocks.peripheral );
             }
-            else if( key.equals( "CC-Cable" ) )
+            else if( key.equalsIgnoreCase( "CC-Cable" ) )
             {
                 remap( mapping, ComputerCraft.Blocks.cable );
             }
-            else if( key.equals( "diskExpanded" ) )
+            else if( key.equalsIgnoreCase( "diskExpanded" ) )
             {
                 mapping.remap( ComputerCraft.Items.diskExpanded );
             }
-            else if( key.equals( "treasureDisk" ) )
+            else if( key.equalsIgnoreCase( "treasureDisk" ) )
             {
                 mapping.remap( ComputerCraft.Items.treasureDisk );
             }
-            else if( key.equals( "pocketComputer" ) )
+            else if( key.equalsIgnoreCase( "pocketComputer" ) )
             {
                 mapping.remap( ComputerCraft.Items.pocketComputer );
             }

src/main/java/dan200/computercraft/shared/proxy/ICCTurtleProxy.java

@@ -11,8 +11,9 @@
 import net.minecraft.entity.Entity;
 import net.minecraft.item.ItemStack;
 import net.minecraftforge.fml.common.event.FMLMissingMappingsEvent;
+import net.minecraft.util.NonNullList;
 
-import java.util.List;
+import javax.annotation.Nonnull;
 
 public interface ICCTurtleProxy
 {
@@ -23,8 +24,8 @@ public interface ICCTurtleProxy
     void registerTurtleUpgrade( ITurtleUpgrade upgrade );
     ITurtleUpgrade getTurtleUpgrade( String id );
     ITurtleUpgrade getTurtleUpgrade( int legacyId );
-    ITurtleUpgrade getTurtleUpgrade( ItemStack item );
-    void addAllUpgradedTurtles( List<ItemStack> list );
+    ITurtleUpgrade getTurtleUpgrade( @Nonnull ItemStack item );
+    void addAllUpgradedTurtles( NonNullList<ItemStack> list );
 
     void setEntityDropConsumer( Entity entity, IEntityDropConsumer consumer );
     void clearEntityDropConsumer( Entity entity );

src/main/java/dan200/computercraft/shared/proxy/IComputerCraftProxy.java

@@ -20,6 +20,7 @@
 import net.minecraft.world.World;
 import net.minecraftforge.fml.common.event.FMLMissingMappingsEvent;
 
+import javax.annotation.Nonnull;
 import java.io.File;
 
 public interface IComputerCraftProxy
@@ -34,7 +35,7 @@ public interface IComputerCraftProxy
     void deleteDisplayLists( int list, int range );
     Object getFixedWidthFontRenderer();
 
-    String getRecordInfo( ItemStack item );
+    String getRecordInfo( @Nonnull ItemStack item );
     void playRecord( SoundEvent record, String recordInfo, World world, BlockPos pos );
 
     Object getDiskDriveGUI( InventoryPlayer inventory, TileDiskDrive drive );

src/main/java/dan200/computercraft/shared/turtle/apis/TurtleAPI.java

@@ -250,9 +250,9 @@ public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull O
                 // getItemCount
                 int slot = parseOptionalSlotNumber( args, 0, m_turtle.getSelectedSlot() );
                 ItemStack stack = m_turtle.getInventory().getStackInSlot( slot );
-                if( stack != null )
+                if( !stack.isEmpty() )
                 {
-                    return new Object[] { stack.stackSize };
+                    return new Object[] { stack.getCount() };
                 }
                 else
                 {
@@ -264,10 +264,10 @@ public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull O
                 // getItemSpace
                 int slot = parseOptionalSlotNumber( args, 0, m_turtle.getSelectedSlot() );
                 ItemStack stack = m_turtle.getInventory().getStackInSlot( slot );
-                if( stack != null )
+                if( !stack.isEmpty() )
                 {
                     return new Object[] {
-                        Math.min( stack.getMaxStackSize(), 64 ) - stack.stackSize
+                        Math.min( stack.getMaxStackSize(), 64 ) - stack.getCount()
                     };
                 }
                 return new Object[] { 64 };
@@ -428,12 +428,12 @@ public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull O
                 // getItemDetail
                 int slot = parseOptionalSlotNumber( args, 0, m_turtle.getSelectedSlot() );
                 ItemStack stack = m_turtle.getInventory().getStackInSlot( slot );
-                if( stack != null && stack.stackSize > 0 )
+                if( !stack.isEmpty() )
                 {
                     Item item = stack.getItem();
                     String name = Item.REGISTRY.getNameForObject( item ).toString();
                     int damage = stack.getItemDamage();
-                    int count = stack.stackSize;
+                    int count = stack.getCount();
 
                     Map<Object, Object> table = new HashMap<Object, Object>();
                     table.put( "name", name );

src/main/java/dan200/computercraft/shared/turtle/blocks/BlockTurtle.java

@@ -152,13 +152,13 @@ else if( this == ComputerCraft.Blocks.turtleExpanded )
     }
 
     @Override
-    public void onBlockPlacedBy( World world, BlockPos pos, IBlockState state, EntityLivingBase player, ItemStack itemstack )
+    public void onBlockPlacedBy( World world, BlockPos pos, IBlockState state, EntityLivingBase player, @Nonnull ItemStack itemstack )
     {
         // Not sure why this is necessary
         TileEntity tile = world.getTileEntity( pos );
         if( tile != null && tile instanceof TileTurtle )
         {
-            tile.setWorldObj( world ); // Not sure why this is necessary
+            tile.setWorld( world ); // Not sure why this is necessary
             tile.setPos( pos ); // Not sure why this is necessary
         }
 

src/main/java/dan200/computercraft/shared/turtle/blocks/TileTurtle.java

@@ -29,10 +29,7 @@
 import net.minecraft.item.ItemStack;
 import net.minecraft.nbt.NBTTagCompound;
 import net.minecraft.nbt.NBTTagList;
-import net.minecraft.util.EnumFacing;
-import net.minecraft.util.EnumHand;
-import net.minecraft.util.ITickable;
-import net.minecraft.util.ResourceLocation;
+import net.minecraft.util.*;
 import net.minecraft.util.math.AxisAlignedBB;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.math.Vec3d;
@@ -68,8 +65,8 @@ enum MoveState
         MOVED
     }
 
-    private ItemStack[] m_inventory;
-    private ItemStack[] m_previousInventory;
+    private NonNullList<ItemStack> m_inventory;
+    private NonNullList<ItemStack> m_previousInventory;
     private final IItemHandlerModifiable m_itemHandler = new InvWrapper( this );
     private boolean m_inventoryChanged;
     private TurtleBrain m_brain;
@@ -77,8 +74,8 @@ enum MoveState
 
     public TileTurtle()
     {
-        m_inventory = new ItemStack[ INVENTORY_SIZE ];
-        m_previousInventory =  new ItemStack[ getSizeInventory() ];
+        m_inventory = NonNullList.withSize( INVENTORY_SIZE, ItemStack.EMPTY );
+        m_previousInventory = NonNullList.withSize( INVENTORY_SIZE, ItemStack.EMPTY );
         m_inventoryChanged = false;
         m_brain = createBrain();
         m_moveState = MoveState.NOT_MOVED;
@@ -97,7 +94,7 @@ protected TurtleBrain createBrain()
     protected final ServerComputer createComputer( int instanceID, int id, int termWidth, int termHeight )
     {
         ServerComputer computer = new ServerComputer(
-            worldObj,
+            getWorld(),
             id,
             m_label,
             instanceID,
@@ -126,15 +123,15 @@ public void destroy()
             super.destroy();
 
             // Drop contents
-            if( !worldObj.isRemote )
+            if( !getWorld().isRemote )
             {
                 int size = getSizeInventory();
                 for( int i=0; i<size; ++i )
                 {
                     ItemStack stack = getStackInSlot( i );
-                    if( stack != null )
+                    if( !stack.isEmpty() )
                     {
-                        WorldUtil.dropItemStack( stack, worldObj, getPos() );
+                        WorldUtil.dropItemStack( stack, getWorld(), getPos() );
                     }
                 }
             }
@@ -144,7 +141,7 @@ public void destroy()
             // Just turn off any redstone we had on
             for( EnumFacing dir : EnumFacing.VALUES )
             {
-                RedstoneUtil.propogateRedstoneOutput( worldObj, getPos(), dir );
+                RedstoneUtil.propogateRedstoneOutput( getWorld(), getPos(), dir );
             }
         }
     }
@@ -182,12 +179,12 @@ public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, flo
 
         // Apply dye
         ItemStack currentItem = player.getHeldItem( EnumHand.MAIN_HAND );
-        if( currentItem != null )
+        if( !currentItem.isEmpty() )
         {
             if( currentItem.getItem() == Items.DYE )
             {
                 // Dye to change turtle colour
-                if( !worldObj.isRemote )
+                if( !getWorld().isRemote )
                 {
                     int dye = (currentItem.getItemDamage() & 0xf);
                     if( m_brain.getDyeColour() != dye )
@@ -195,7 +192,7 @@ public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, flo
                         m_brain.setDyeColour( dye );
                         if( !player.capabilities.isCreativeMode )
                         {
-                            currentItem.stackSize--;
+                            currentItem.shrink( 1 );
                         }
                     }
                 }
@@ -204,7 +201,7 @@ public boolean onActivate( EntityPlayer player, EnumFacing side, float hitX, flo
             else if( currentItem.getItem() == Items.WATER_BUCKET && m_brain.getColour() != -1 )
             {
                 // Water to remove turtle colour
-                if( !worldObj.isRemote )
+                if( !getWorld().isRemote )
                 {
                     if( m_brain.getColour() != -1 )
                     {
@@ -279,7 +276,7 @@ public void update()
         m_brain.update();
         synchronized( m_inventory )
         {
-            if( !worldObj.isRemote && m_inventoryChanged )
+            if( !getWorld().isRemote && m_inventoryChanged )
             {
                 IComputer computer = getComputer();
                 if( computer != null )
@@ -290,7 +287,7 @@ public void update()
                 m_inventoryChanged = false;
                 for( int n=0; n<getSizeInventory(); ++n )
                 {
-                    m_previousInventory[n] = InventoryUtil.copyItem( getStackInSlot( n ) );
+                    m_previousInventory.set( n, InventoryUtil.copyItem( getStackInSlot( n ) ) );
                 }
             }
         }
@@ -338,16 +335,16 @@ public void readFromNBT( NBTTagCompound nbttagcompound )
 
         // Read inventory
         NBTTagList nbttaglist = nbttagcompound.getTagList("Items", Constants.NBT.TAG_COMPOUND);
-        m_inventory = new ItemStack[ INVENTORY_SIZE ];
-        m_previousInventory = new ItemStack[ getSizeInventory() ];
+        m_inventory = NonNullList.withSize( INVENTORY_SIZE, ItemStack.EMPTY );
+        m_previousInventory = NonNullList.withSize( INVENTORY_SIZE, ItemStack.EMPTY );
         for( int i=0; i<nbttaglist.tagCount(); ++i )
         {
             NBTTagCompound itemtag = nbttaglist.getCompoundTagAt( i );
             int slot = itemtag.getByte("Slot") & 0xff;
             if( slot >= 0 && slot < getSizeInventory() )
             {
-                m_inventory[slot] = ItemStack.loadItemStackFromNBT( itemtag );
-                m_previousInventory[slot] = InventoryUtil.copyItem( m_inventory[slot] );
+                m_inventory.set( slot, new ItemStack( itemtag ) );
+                m_previousInventory.set( slot, InventoryUtil.copyItem( m_inventory.get( slot ) ) );
             }
         }
 
@@ -365,11 +362,11 @@ public NBTTagCompound writeToNBT( NBTTagCompound nbttagcompound )
         NBTTagList nbttaglist = new NBTTagList();
         for( int i=0; i<INVENTORY_SIZE; ++i )
         {
-            if( m_inventory[i] != null )
+            if( !m_inventory.get(i).isEmpty() )
             {
                 NBTTagCompound itemtag = new NBTTagCompound();
                 itemtag.setByte( "Slot", (byte)i );
-                m_inventory[i].writeToNBT(itemtag);
+                m_inventory.get(i).writeToNBT(itemtag);
                 nbttaglist.appendTag(itemtag);
             }
         }
@@ -459,6 +456,17 @@ public int getSizeInventory()
         return INVENTORY_SIZE;
     }
 
+    @Override
+    public boolean isEmpty()
+    {
+        for( ItemStack stack : m_inventory )
+        {
+            if( !stack.isEmpty() ) return false;
+        }
+        return true;
+    }
+
+    @Nonnull
     @Override
     public ItemStack getStackInSlot( int slot )
     {
@@ -466,42 +474,44 @@ public ItemStack getStackInSlot( int slot )
         {
             synchronized( m_inventory )
             {
-                return m_inventory[ slot ];
+                return m_inventory.get( slot );
             }
         }
-        return null;
+        return ItemStack.EMPTY;
     }
 
+    @Nonnull
     @Override
     public ItemStack removeStackFromSlot( int slot )
     {
         synchronized( m_inventory )
         {
             ItemStack result = getStackInSlot( slot );
-            setInventorySlotContents( slot, null );
+            setInventorySlotContents( slot, ItemStack.EMPTY );
             return result;
         }
     }
 
+    @Nonnull
     @Override
     public ItemStack decrStackSize( int slot, int count )
     {
         if( count == 0 )
         {
-            return null;
+            return ItemStack.EMPTY;
         }
 
         synchronized( m_inventory )
         {
             ItemStack stack = getStackInSlot( slot );
-            if( stack == null )
+            if( stack.isEmpty() )
             {
-                return null;
+                return ItemStack.EMPTY;
             }
 
-            if( stack.stackSize <= count )
+            if( stack.getCount() <= count )
             {
-                setInventorySlotContents( slot, null );
+                setInventorySlotContents( slot, ItemStack.EMPTY );
                 return stack;
             }
 
@@ -512,15 +522,15 @@ public ItemStack decrStackSize( int slot, int count )
     }
 
     @Override
-    public void setInventorySlotContents( int i, ItemStack stack )
+    public void setInventorySlotContents( int i, @Nonnull ItemStack stack )
     {
         if( i >= 0 && i < INVENTORY_SIZE )
         {
             synchronized( m_inventory )
             {
-                if( !InventoryUtil.areItemsEqual( stack, m_inventory[ i ] ) )
+                if( !InventoryUtil.areItemsEqual( stack, m_inventory.get( i ) ) )
                 {
-                    m_inventory[ i ] = stack;
+                    m_inventory.set( i, stack );
                     onInventoryDefinitelyChanged();
                 }
             }
@@ -535,9 +545,9 @@ public void clear()
             boolean changed = false;
             for( int i = 0; i < INVENTORY_SIZE; ++i )
             {
-                if( m_inventory[i] != null )
+                if( !m_inventory.get( i ).isEmpty() )
                 {
-                    m_inventory[i] = null;
+                    m_inventory.set( i, ItemStack.EMPTY );
                     changed = true;
                 }
             }
@@ -625,7 +635,7 @@ public void markDirty()
             {
                 for( int n=0; n<getSizeInventory(); ++n )
                 {
-                    if( !ItemStack.areItemStacksEqual( getStackInSlot( n ), m_previousInventory[n] ) )
+                    if( !ItemStack.areItemStacksEqual( getStackInSlot( n ), m_previousInventory.get( n ) ) )
                     {
                         m_inventoryChanged = true;
                         break;
@@ -636,7 +646,7 @@ public void markDirty()
     }
 
     @Override
-    public boolean isUseableByPlayer( @Nonnull EntityPlayer player )
+    public boolean isUsableByPlayer( @Nonnull EntityPlayer player )
     {
         return isUsable( player, false );
     }
@@ -727,7 +737,7 @@ public boolean hasCapability( @Nonnull Capability<?> capability, @Nullable EnumF
         return capability == ITEM_HANDLER_CAPABILITY ||  super.hasCapability( capability, facing );
     }
 
-    @Nonnull
+    @Nullable
     @Override
     public <T> T getCapability( @Nonnull Capability<T> capability, @Nullable EnumFacing facing )
     {

src/main/java/dan200/computercraft/shared/turtle/core/TurtleBrain.java

@@ -20,6 +20,7 @@
 import net.minecraft.block.Block;
 import net.minecraft.block.state.IBlockState;
 import net.minecraft.entity.Entity;
+import net.minecraft.entity.MoverType;
 import net.minecraft.inventory.IInventory;
 import net.minecraft.nbt.NBTTagCompound;
 import net.minecraft.tileentity.TileEntity;
@@ -286,11 +287,11 @@ public void readFromNBT( NBTTagCompound nbttagcompound )
         m_upgradeNBTData.clear();
         if( nbttagcompound.hasKey( "leftUpgradeNBT" ) )
         {
-            m_upgradeNBTData.put( TurtleSide.Left, (NBTTagCompound) nbttagcompound.getCompoundTag( "leftUpgradeNBT" ).copy() );
+            m_upgradeNBTData.put( TurtleSide.Left, nbttagcompound.getCompoundTag( "leftUpgradeNBT" ).copy() );
         }
         if( nbttagcompound.hasKey( "rightUpgradeNBT" ) )
         {
-            m_upgradeNBTData.put( TurtleSide.Right, (NBTTagCompound) nbttagcompound.getCompoundTag( "rightUpgradeNBT" ).copy() );
+            m_upgradeNBTData.put( TurtleSide.Right, nbttagcompound.getCompoundTag( "rightUpgradeNBT" ).copy() );
         }
     }
 
@@ -420,11 +421,11 @@ public void readDescription( NBTTagCompound nbttagcompound )
         m_upgradeNBTData.clear();
         if( nbttagcompound.hasKey( "leftUpgradeNBT" ) )
         {
-            m_upgradeNBTData.put( TurtleSide.Left, (NBTTagCompound) nbttagcompound.getCompoundTag( "leftUpgradeNBT" ).copy() );
+            m_upgradeNBTData.put( TurtleSide.Left, nbttagcompound.getCompoundTag( "leftUpgradeNBT" ).copy() );
         }
         if( nbttagcompound.hasKey( "rightUpgradeNBT" ) )
         {
-            m_upgradeNBTData.put( TurtleSide.Right, (NBTTagCompound)nbttagcompound.getCompoundTag( "rightUpgradeNBT" ).copy() );
+            m_upgradeNBTData.put( TurtleSide.Right, nbttagcompound.getCompoundTag( "rightUpgradeNBT" ).copy() );
         }
 
         // Colour
@@ -515,7 +516,7 @@ public boolean teleportTo( @Nonnull World world, @Nonnull BlockPos pos )
                     {
                         // Copy the old turtle state into the new turtle
                         TileTurtle newTurtle = (TileTurtle)newTile;
-                        newTurtle.setWorldObj( world );
+                        newTurtle.setWorld( world );
                         newTurtle.setPos( pos );
                         newTurtle.transferStateFrom( oldOwner );
                         newTurtle.createServerComputer().setWorld( world );
@@ -1160,7 +1161,7 @@ private void updateAnimation()
                         double pushStepZ = (double) moveDir.getFrontOffsetZ() * pushStep;
                         for (Entity entity : list)
                         {
-                            entity.moveEntity( pushStepX, pushStepY, pushStepZ );
+                            entity.move( MoverType.PISTON, pushStepX, pushStepY, pushStepZ );
                         }
                     }
                 }

src/main/java/dan200/computercraft/shared/turtle/core/TurtleCompareCommand.java

@@ -21,6 +21,7 @@
 
 import javax.annotation.Nonnull;
 import java.lang.reflect.Method;
+import java.util.List;
 
 public class TurtleCompareCommand implements ITurtleCommand
 {
@@ -46,7 +47,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
         BlockPos oldPosition = turtle.getPosition();
         BlockPos newPosition = oldPosition.offset( direction );
 
-        ItemStack lookAtStack = null;
+        ItemStack lookAtStack = ItemStack.EMPTY;
         if( WorldUtil.isBlockInWorld( world, newPosition ) )
         {
             if( !world.isAirBlock( newPosition ) )
@@ -61,8 +62,8 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
                         try
                         {
                             Method method = ReflectionHelper.findMethod(
-                                Block.class, lookAtBlock,
-                                new String[] { "func_180643_i", "createStackedBlock" },
+                                Block.class,
+                                "func_180643_i", "getSilkTouchDrop",
                                 IBlockState.class
                             );
                             lookAtStack = (ItemStack) method.invoke( lookAtBlock, lookAtState );
@@ -74,9 +75,9 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
 
                     // See if the block drops anything with the same ID as itself
                     // (try 5 times to try and beat random number generators)
-                    for( int i=0; (i<5) && (lookAtStack == null); ++i )
+                    for( int i=0; (i<5) && lookAtStack.isEmpty(); ++i )
                     {
-                        java.util.List<ItemStack> drops = lookAtBlock.getDrops( world, newPosition, lookAtState, 0 );
+                        List<ItemStack> drops = lookAtBlock.getDrops( world, newPosition, lookAtState, 0 );
                         if( drops != null && drops.size() > 0 )
                         {
                             for( ItemStack drop : drops )
@@ -91,7 +92,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
                     }
 
                     // Last resort: roll our own (which will probably be wrong)
-                    if( lookAtStack == null )
+                    if( lookAtStack.isEmpty() )
                     {
                         Item item = Item.getItemFromBlock( lookAtBlock );
                         if( item != null && item.getHasSubtypes() )
@@ -108,11 +109,11 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
         }
 
         // Compare them
-        if( selectedStack == null && lookAtStack == null )
+        if( selectedStack.isEmpty() && lookAtStack.isEmpty() )
         {
             return TurtleCommandResult.success();
         }
-        else if( selectedStack != null && lookAtStack != null )
+        else if( !selectedStack.isEmpty() && lookAtStack != null )
         {
             if( selectedStack.getItem() == lookAtStack.getItem() )
             {

src/main/java/dan200/computercraft/shared/turtle/core/TurtleCraftCommand.java

@@ -41,7 +41,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
             for( ItemStack stack : results )
             {
                 ItemStack remainder = InventoryUtil.storeItems( stack, turtle.getItemHandler(), turtle.getSelectedSlot() );
-                if( remainder != null )
+                if( !remainder.isEmpty() )
                 {
                     // Drop the remainder
                     BlockPos position = turtle.getPosition();

src/main/java/dan200/computercraft/shared/turtle/core/TurtleDropCommand.java

@@ -12,10 +12,9 @@
 import dan200.computercraft.api.turtle.TurtleCommandResult;
 import dan200.computercraft.shared.util.InventoryUtil;
 import dan200.computercraft.shared.util.WorldUtil;
-import net.minecraft.inventory.IInventory;
 import net.minecraft.item.ItemStack;
-import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.EnumFacing;
+import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.World;
 import net.minecraftforge.items.IItemHandler;
 
@@ -48,7 +47,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
 
         // Get things to drop
         ItemStack stack = InventoryUtil.takeItems( m_quantity, turtle.getItemHandler(), turtle.getSelectedSlot(), 1, turtle.getSelectedSlot() );
-        if( stack == null )
+        if( stack.isEmpty() )
         {
             return TurtleCommandResult.failure( "No items to drop" );
         }
@@ -64,7 +63,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
         {
             // Drop the item into the inventory
             ItemStack remainder = InventoryUtil.storeItems( stack, inventory );
-            if( remainder != null )
+            if( !remainder.isEmpty() )
             {
                 // Put the remainder back in the turtle
                 InventoryUtil.storeItems( remainder, turtle.getItemHandler(), turtle.getSelectedSlot() );

src/main/java/dan200/computercraft/shared/turtle/core/TurtleEquipCommand.java

@@ -11,7 +11,6 @@
 import dan200.computercraft.shared.proxy.CCTurtleProxyCommon;
 import dan200.computercraft.shared.util.InventoryUtil;
 import dan200.computercraft.shared.util.WorldUtil;
-import net.minecraft.inventory.IInventory;
 import net.minecraft.item.ItemStack;
 import net.minecraft.util.math.BlockPos;
 import net.minecraftforge.items.IItemHandler;
@@ -36,7 +35,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
         ItemStack newUpgradeStack;
         IItemHandler inventory = turtle.getItemHandler();
         ItemStack selectedStack = inventory.getStackInSlot( turtle.getSelectedSlot() );
-        if( selectedStack != null )
+        if( !selectedStack.isEmpty() )
         {
             newUpgradeStack = selectedStack.copy();
             newUpgrade = ComputerCraft.getTurtleUpgrade( newUpgradeStack );
@@ -57,7 +56,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
         if( oldUpgrade != null )
         {
             ItemStack craftingItem = oldUpgrade.getCraftingItem();
-            oldUpgradeStack = (craftingItem != null) ? craftingItem.copy() : null;
+            oldUpgradeStack = !craftingItem.isEmpty() ? craftingItem.copy() : null;
         }
         else
         {
@@ -74,7 +73,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
         {
             // Store old upgrades item
             ItemStack remainder = InventoryUtil.storeItems( oldUpgradeStack, inventory, turtle.getSelectedSlot() );
-            if( remainder != null )
+            if( !remainder.isEmpty() )
             {
                 // If there's no room for the items, drop them
                 BlockPos position = turtle.getPosition();

src/main/java/dan200/computercraft/shared/turtle/core/TurtleMoveCommand.java

@@ -89,7 +89,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
                                 (double) direction.getFrontOffsetY(),
                                 (double) direction.getFrontOffsetZ()
                             );
-                            if( !oldWorld.getCollisionBoxes( pushedBB ).isEmpty() )
+                            if( !oldWorld.getCollisionBoxes( null, pushedBB ).isEmpty() )
                             {
                                 return TurtleCommandResult.failure( "Movement obstructed" );
                             }

src/main/java/dan200/computercraft/shared/turtle/core/TurtlePlaceCommand.java

@@ -55,7 +55,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
     {
         // Get thing to place
         ItemStack stack = turtle.getInventory().getStackInSlot( turtle.getSelectedSlot() );
-        if( stack == null )
+        if( stack.isEmpty() )
         {
             return TurtleCommandResult.failure( "No items to place" );
         }
@@ -112,7 +112,7 @@ else if( stack.getItem() instanceof ItemBlock )
         }
     }
 
-    public static ItemStack deploy( ItemStack stack, ITurtleAccess turtle, EnumFacing direction, Object[] extraArguments, String[] o_errorMessage )
+    public static ItemStack deploy( @Nonnull ItemStack stack, ITurtleAccess turtle, EnumFacing direction, Object[] extraArguments, String[] o_errorMessage )
     {
         // Create a fake player, and orient it appropriately
         BlockPos playerPosition = WorldUtil.moveCoords( turtle.getPosition(), direction );
@@ -204,7 +204,8 @@ public static void orientPlayer( ITurtleAccess turtle, TurtlePlayer turtlePlayer
         turtlePlayer.prevRotationYawHead = turtlePlayer.rotationYawHead;
     }
 
-    private static ItemStack deployOnEntity( ItemStack stack, final ITurtleAccess turtle, TurtlePlayer turtlePlayer, EnumFacing direction, Object[] extraArguments, String[] o_errorMessage )
+    @Nonnull
+    private static ItemStack deployOnEntity( @Nonnull ItemStack stack, final ITurtleAccess turtle, TurtlePlayer turtlePlayer, EnumFacing direction, Object[] extraArguments, String[] o_errorMessage )
     {
         // See if there is an entity present
         final World world = turtle.getWorld();
@@ -227,10 +228,10 @@ private static ItemStack deployOnEntity( ItemStack stack, final ITurtleAccess tu
         ComputerCraft.setEntityDropConsumer( hitEntity, new IEntityDropConsumer()
         {
             @Override
-            public void consumeDrop( Entity entity, ItemStack drop )
+            public void consumeDrop( Entity entity, @Nonnull ItemStack drop )
             {
                 ItemStack remainder = InventoryUtil.storeItems( drop, turtle.getItemHandler(), turtle.getSelectedSlot() );
-                if( remainder != null )
+                if( !remainder.isEmpty() )
                 {
                     WorldUtil.dropItemStack( remainder, world, position, turtle.getDirection().getOpposite() );
                 }
@@ -239,25 +240,34 @@ public void consumeDrop( Entity entity, ItemStack drop )
 
         // Place on the entity
         boolean placed = false;
-        if( !ForgeHooks.onInteractEntityAt( turtlePlayer, hitEntity, hitPos, stack, EnumHand.MAIN_HAND ) &&
-            hitEntity.applyPlayerInteraction( turtlePlayer, hitPos, stackCopy, EnumHand.MAIN_HAND ) == EnumActionResult.SUCCESS )
+        EnumActionResult cancelResult = ForgeHooks.onInteractEntityAtAction( turtlePlayer, hitEntity, hitPos, EnumHand.MAIN_HAND );
+        if( cancelResult == null )
+        {
+            cancelResult = hitEntity.applyPlayerInteraction( turtlePlayer, hitPos, EnumHand.MAIN_HAND );
+        }
+
+        if( cancelResult == EnumActionResult.SUCCESS )
         {
             placed = true;
-            turtlePlayer.loadInventory( stackCopy );
         }
-        else if( !ForgeHooks.onInteractEntity( turtlePlayer, hitEntity, stack, EnumHand.MAIN_HAND ) )
+        else
         {
-            // See EntityPlayer.interact
-            if( hitEntity.processInitialInteract( turtlePlayer, stackCopy, EnumHand.MAIN_HAND ) )
+            // See EntityPlayer.interactOn
+            cancelResult = ForgeHooks.onInteractEntityAction( turtlePlayer, hitEntity, EnumHand.MAIN_HAND );
+            if( cancelResult == EnumActionResult.SUCCESS )
             {
                 placed = true;
             }
-            else if( hitEntity instanceof EntityLivingBase )
+            else if( cancelResult == null )
             {
-                placed = stackCopy.interactWithEntity( turtlePlayer, (EntityLivingBase) hitEntity, EnumHand.MAIN_HAND );
-                if( placed )
+                if( hitEntity.processInitialInteract( turtlePlayer, EnumHand.MAIN_HAND ) )
                 {
-                    turtlePlayer.loadInventory( stackCopy );
+                    placed = true;
+                }
+                else if( hitEntity instanceof EntityLivingBase )
+                {
+                    placed = stackCopy.interactWithEntity( turtlePlayer, (EntityLivingBase) hitEntity, EnumHand.MAIN_HAND );
+                    if( placed ) turtlePlayer.loadInventory( stackCopy );
                 }
             }
         }
@@ -267,21 +277,21 @@ else if( hitEntity instanceof EntityLivingBase )
 
         // Put everything we collected into the turtles inventory, then return
         ItemStack remainder = turtlePlayer.unloadInventory( turtle );
-        if( !placed && (remainder != null && ItemStack.areItemStacksEqual( stack, remainder )) )
+        if( !placed && ItemStack.areItemStacksEqual( stack, remainder ) )
         {
             return stack;
         }
-        else if( remainder != null && remainder.stackSize > 0 )
+        else if( !remainder.isEmpty() )
         {
             return remainder;
         }
         else
         {
-            return null;
+            return ItemStack.EMPTY;
         }
     }
 
-    private static boolean canDeployOnBlock( ItemStack stack, ITurtleAccess turtle, TurtlePlayer player, BlockPos position, EnumFacing side, boolean allowReplaceable, String[] o_errorMessage )
+    private static boolean canDeployOnBlock( @Nonnull ItemStack stack, ITurtleAccess turtle, TurtlePlayer player, BlockPos position, EnumFacing side, boolean allowReplaceable, String[] o_errorMessage )
     {
         World world = turtle.getWorld();
         if( WorldUtil.isBlockInWorld( world, position ) &&
@@ -330,7 +340,8 @@ private static boolean canDeployOnBlock( ItemStack stack, ITurtleAccess turtle,
         return false;
     }
 
-    private static ItemStack deployOnBlock( ItemStack stack, ITurtleAccess turtle, TurtlePlayer turtlePlayer, BlockPos position, EnumFacing side, Object[] extraArguments, boolean allowReplace, String[] o_errorMessage )
+    @Nonnull
+    private static ItemStack deployOnBlock( @Nonnull ItemStack stack, ITurtleAccess turtle, TurtlePlayer turtlePlayer, BlockPos position, EnumFacing side, Object[] extraArguments, boolean allowReplace, String[] o_errorMessage )
     {
         // Check if there's something suitable to place onto
         if( !canDeployOnBlock( stack, turtle, turtlePlayer, position, side, allowReplace, o_errorMessage ) )
@@ -362,10 +373,10 @@ private static ItemStack deployOnBlock( ItemStack stack, ITurtleAccess turtle, T
 
 
         // See PlayerInteractionManager.processRightClickBlock
-        PlayerInteractEvent.RightClickBlock event = ForgeHooks.onRightClickBlock( turtlePlayer, EnumHand.MAIN_HAND, stackCopy, position, side, new Vec3d( hitX, hitY, hitZ ) );
+        PlayerInteractEvent.RightClickBlock event = ForgeHooks.onRightClickBlock( turtlePlayer, EnumHand.MAIN_HAND, position, side, new Vec3d( hitX, hitY, hitZ ) );
         if( !event.isCanceled() )
         {
-            if( item.onItemUseFirst( stackCopy, turtlePlayer, turtle.getWorld(), position, side, hitX, hitY, hitZ, EnumHand.MAIN_HAND ) == EnumActionResult.SUCCESS )
+            if( item.onItemUseFirst( turtlePlayer, turtle.getWorld(), position, side, hitX, hitY, hitZ, EnumHand.MAIN_HAND ) == EnumActionResult.SUCCESS )
             {
                 placed = true;
                 turtlePlayer.loadInventory( stackCopy );
@@ -378,14 +389,21 @@ else if( event.getUseItem() != Event.Result.DENY &&
             }
         }
 
-        if( !placed && (item instanceof ItemBucket || item instanceof ItemBoat || item instanceof ItemLilyPad || item instanceof ItemGlassBottle)
-            && ForgeHooks.onItemRightClick( turtlePlayer, EnumHand.MAIN_HAND, stackCopy ) )
+        if( !placed && (item instanceof ItemBucket || item instanceof ItemBoat || item instanceof ItemLilyPad || item instanceof ItemGlassBottle) )
         {
-            ActionResult<ItemStack> result = stackCopy.useItemRightClick( turtle.getWorld(), turtlePlayer, EnumHand.MAIN_HAND );
-            if( result.getType() == EnumActionResult.SUCCESS && !ItemStack.areItemStacksEqual( stack, result.getResult() ) )
+            EnumActionResult actionResult = ForgeHooks.onItemRightClickAction( turtlePlayer, EnumHand.MAIN_HAND );
+            if( actionResult == EnumActionResult.SUCCESS )
             {
                 placed = true;
-                turtlePlayer.loadInventory( result.getResult() );
+            }
+            else if( actionResult == null )
+            {
+                ActionResult<ItemStack> result = stackCopy.useItemRightClick( turtle.getWorld(), turtlePlayer, EnumHand.MAIN_HAND );
+                if( result.getType() == EnumActionResult.SUCCESS && !ItemStack.areItemStacksEqual( stack, result.getResult() ) )
+                {
+                    placed = true;
+                    turtlePlayer.loadInventory( result.getResult() );
+                }
             }
         }
 
@@ -433,17 +451,17 @@ else if( event.getUseItem() != Event.Result.DENY &&
 
         // Put everything we collected into the turtles inventory, then return
         ItemStack remainder = turtlePlayer.unloadInventory( turtle );
-        if( !placed && (remainder != null && ItemStack.areItemStacksEqual( stack, remainder )) )
+        if( !placed && ItemStack.areItemStacksEqual( stack, remainder ) )
         {
             return stack;
         }
-        else if( remainder != null && remainder.stackSize > 0 )
+        else if( !remainder.isEmpty() )
         {
             return remainder;
         }
         else
         {
-            return null;
+            return ItemStack.EMPTY;
         }
     }
 }

src/main/java/dan200/computercraft/shared/turtle/core/TurtlePlayer.java

@@ -13,8 +13,9 @@
 import net.minecraft.entity.Entity;
 import net.minecraft.item.ItemStack;
 import net.minecraft.tileentity.TileEntitySign;
-import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.EnumFacing;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.world.World;
 import net.minecraft.world.WorldServer;
 import net.minecraftforge.common.util.FakePlayer;
 
@@ -28,12 +29,18 @@ public class TurtlePlayer extends FakePlayer
         "ComputerCraft"
     );
 
+    @Deprecated
+    public TurtlePlayer( World world )
+    {
+        this( (WorldServer) world );
+    }
+
     public TurtlePlayer( WorldServer world )
     {
         super( world, s_profile );
     }
 
-    public void loadInventory( ItemStack currentStack )
+    public void loadInventory( @Nonnull ItemStack currentStack )
     {
         // Load up the fake inventory
         inventory.currentItem = 0;
@@ -44,7 +51,7 @@ public ItemStack unloadInventory( ITurtleAccess turtle )
     {
         // Get the item we placed with
         ItemStack results = inventory.getStackInSlot( 0 );
-        inventory.setInventorySlotContents( 0, null );
+        inventory.setInventorySlotContents( 0, ItemStack.EMPTY );
 
         // Store (or drop) anything else we found
         BlockPos dropPosition = turtle.getPosition();
@@ -52,14 +59,14 @@ public ItemStack unloadInventory( ITurtleAccess turtle )
         for( int i=0; i<inventory.getSizeInventory(); ++i )
         {
             ItemStack stack = inventory.getStackInSlot( i );
-            if( stack != null )
+            if( !stack.isEmpty() )
             {
                 ItemStack remainder = InventoryUtil.storeItems( stack, turtle.getItemHandler(), turtle.getSelectedSlot() );
-                if( remainder != null )
+                if( !remainder.isEmpty() )
                 {
                     WorldUtil.dropItemStack( remainder, turtle.getWorld(), dropPosition, dropDirection );
                 }
-                inventory.setInventorySlotContents( i, null );
+                inventory.setInventorySlotContents( i, ItemStack.EMPTY );
             }
         }
         inventory.markDirty();

src/main/java/dan200/computercraft/shared/turtle/core/TurtleRefuelCommand.java

@@ -33,7 +33,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
         {
             // If limit is zero, just check the item is combustible
             ItemStack dummyStack = turtle.getInventory().getStackInSlot( turtle.getSelectedSlot() );
-            if( dummyStack != null )
+            if( !dummyStack.isEmpty() )
             {
                 return refuel( turtle, dummyStack, true );
             }
@@ -43,7 +43,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
             // Otherwise, refuel for real
             // Remove items from inventory
             ItemStack stack = InventoryUtil.takeItems( m_limit, turtle.getItemHandler(), turtle.getSelectedSlot(), 1, turtle.getSelectedSlot() );
-            if( stack != null )
+            if( !stack.isEmpty() )
             {
                 TurtleCommandResult result = refuel( turtle, stack, false );
                 if( !result.isSuccess() )
@@ -57,12 +57,12 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
         return TurtleCommandResult.failure( "No items to combust" );
     }
 
-    private int getFuelPerItem( ItemStack stack )
+    private int getFuelPerItem( @Nonnull ItemStack stack )
     {
         return (TileEntityFurnace.getItemBurnTime( stack ) * 5) / 100;
     }
 
-    private TurtleCommandResult refuel( ITurtleAccess turtle, ItemStack stack, boolean testOnly )
+    private TurtleCommandResult refuel( ITurtleAccess turtle, @Nonnull ItemStack stack, boolean testOnly )
     {
         // Check if item is fuel
         int fuelPerItem = getFuelPerItem( stack );
@@ -74,14 +74,14 @@ private TurtleCommandResult refuel( ITurtleAccess turtle, ItemStack stack, boole
         if( !testOnly )
         {
             // Determine fuel to give and replacement item to leave behind
-            int fuelToGive = fuelPerItem * stack.stackSize;
+            int fuelToGive = fuelPerItem * stack.getCount();
             ItemStack replacementStack = stack.getItem().getContainerItem( stack );
 
             // Update fuel level
             turtle.addFuel( fuelToGive );
 
             // Store the replacement item in the inventory
-            if( replacementStack != null )
+            if( !replacementStack.isEmpty() )
             {
                 InventoryUtil.storeItems( replacementStack, turtle.getItemHandler(), turtle.getSelectedSlot() );
             }

src/main/java/dan200/computercraft/shared/turtle/core/TurtleSuckCommand.java

@@ -14,11 +14,10 @@
 import dan200.computercraft.shared.util.WorldUtil;
 import net.minecraft.entity.Entity;
 import net.minecraft.entity.item.EntityItem;
-import net.minecraft.inventory.IInventory;
 import net.minecraft.item.ItemStack;
+import net.minecraft.util.EnumFacing;
 import net.minecraft.util.math.AxisAlignedBB;
 import net.minecraft.util.math.BlockPos;
-import net.minecraft.util.EnumFacing;
 import net.minecraft.world.World;
 import net.minecraftforge.items.IItemHandler;
 
@@ -61,11 +60,11 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
         {
             // Take from inventory of thing in front
             ItemStack stack = InventoryUtil.takeItems( m_quantity, inventory );
-            if( stack != null )
+            if( !stack.isEmpty() )
             {
                 // Try to place into the turtle
                 ItemStack remainder = InventoryUtil.storeItems( stack, turtle.getItemHandler(), turtle.getSelectedSlot() );
-                if( remainder != null )
+                if( !remainder.isEmpty() )
                 {
                     // Put the remainder back in the inventory
                     InventoryUtil.storeItems( remainder, inventory );
@@ -106,7 +105,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
                         ItemStack stack = entityItem.getEntityItem().copy();
                         ItemStack storeStack;
                         ItemStack leaveStack;
-                        if( stack.stackSize > m_quantity )
+                        if( stack.getCount() > m_quantity )
                         {
                             storeStack = stack.splitStack( m_quantity );
                             leaveStack = stack;
@@ -114,27 +113,27 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
                         else
                         {
                             storeStack = stack;
-                            leaveStack = null;
+                            leaveStack = ItemStack.EMPTY;
                         }
                         ItemStack remainder = InventoryUtil.storeItems( storeStack, turtle.getItemHandler(), turtle.getSelectedSlot() );
                         if( remainder != storeStack )
                         {
                             storedItems = true;
-                            if( remainder == null && leaveStack == null )
+                            if( remainder.isEmpty() && leaveStack.isEmpty() )
                             {
                                 entityItem.setDead();
                             }
-                            else if( remainder == null )
+                            else if( remainder.isEmpty() )
                             {
                                 entityItem.setEntityItemStack( leaveStack );
                             }
-                            else if( leaveStack == null )
+                            else if( leaveStack.isEmpty() )
                             {
                                 entityItem.setEntityItemStack( remainder );
                             }
                             else
                             {
-                                leaveStack.stackSize += remainder.stackSize;
+                                leaveStack.grow( remainder.getCount() );
                                 entityItem.setEntityItemStack( leaveStack );
                             }
                             break;

src/main/java/dan200/computercraft/shared/turtle/core/TurtleTransferToCommand.java

@@ -32,7 +32,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
     {
         // Take stack
         ItemStack stack = InventoryUtil.takeItems( m_quantity, turtle.getItemHandler(), turtle.getSelectedSlot(), 1, turtle.getSelectedSlot() );
-        if( stack == null )
+        if( stack.isEmpty() )
         {
             turtle.playAnimation( TurtleAnimation.Wait );
             return TurtleCommandResult.success();
@@ -40,7 +40,7 @@ public TurtleCommandResult execute( @Nonnull ITurtleAccess turtle )
 
         // Store stack
         ItemStack remainder = InventoryUtil.storeItems( stack, turtle.getItemHandler(), m_slot, 1, m_slot );
-        if( remainder != null )
+        if( !remainder.isEmpty() )
         {
             // Put the remainder back
             InventoryUtil.storeItems( remainder, turtle.getItemHandler(), turtle.getSelectedSlot(), 1, turtle.getSelectedSlot() );

src/main/java/dan200/computercraft/shared/turtle/entity/TurtleVisionCamera.java

@@ -88,21 +88,23 @@ else if( yawDifference < -180.0f )
 
     // EntityLivingBase overrides:
 
+    @Nonnull
     @Override
     public ItemStack getHeldItem( EnumHand hand )
     {
-        return null;
+        return ItemStack.EMPTY;
     }
 
     @Override
-    public void setItemStackToSlot( @Nonnull EntityEquipmentSlot slot, ItemStack stack)
+    public void setItemStackToSlot( @Nonnull EntityEquipmentSlot slot, @Nonnull ItemStack stack )
     {
     }
 
+    @Nonnull
     @Override
-    public ItemStack getItemStackFromSlot( @Nonnull EntityEquipmentSlot slot)
+    public ItemStack getItemStackFromSlot( @Nonnull EntityEquipmentSlot slot )
     {
-        return null;
+        return ItemStack.EMPTY;
     }
 
     @Nonnull

src/main/java/dan200/computercraft/shared/turtle/inventory/ContainerTurtle.java

@@ -138,45 +138,47 @@ public boolean canInteractWith( @Nonnull EntityPlayer player )
         TileTurtle turtle = ((TurtleBrain)m_turtle).getOwner();
         if( turtle != null )
         {
-            return turtle.isUseableByPlayer( player );
+            return turtle.isUsableByPlayer( player );
         }
         return false;
     }
 
+    @Nonnull
     protected ItemStack tryItemMerge( EntityPlayer player, int slotNum, int firstSlot, int lastSlot, boolean reverse )
     {
         Slot slot = inventorySlots.get( slotNum );
-        ItemStack originalStack = null;
+        ItemStack originalStack = ItemStack.EMPTY;
         if( slot != null && slot.getHasStack() )
         {
             ItemStack clickedStack = slot.getStack();
             originalStack = clickedStack.copy();
             if( !mergeItemStack( clickedStack, firstSlot, lastSlot, reverse ) )
             {
-                return null;
+                return ItemStack.EMPTY;
             }
 
-            if( clickedStack.stackSize == 0 )
+            if( clickedStack.isEmpty() )
             {
-                slot.putStack( null );
+                slot.putStack( ItemStack.EMPTY );
             }
             else
             {
                 slot.onSlotChanged();
             }
 
-            if( clickedStack.stackSize != originalStack.stackSize )
+            if( clickedStack.getCount() != originalStack.getCount() )
             {
-                slot.onPickupFromSlot( player, clickedStack );
+                slot.onTake( player, clickedStack );
             }
             else
             {
-                return null;
+                return ItemStack.EMPTY;
             }
         }
         return originalStack;
     }
 
+    @Nonnull
     @Override
     public ItemStack transferStackInSlot( EntityPlayer player, int slotNum )
     {
@@ -188,7 +190,7 @@ else if( slotNum >= 16 )
         {
             return tryItemMerge( player, slotNum, 0, 16, false );
         }
-        return null;
+        return ItemStack.EMPTY;
     }
 
     @Nullable

src/main/java/dan200/computercraft/shared/turtle/items/ITurtleItem.java

@@ -13,9 +13,12 @@
 import net.minecraft.item.ItemStack;
 import net.minecraft.util.ResourceLocation;
 
+import javax.annotation.Nonnull;
+
 public interface ITurtleItem extends IComputerItem, IColouredItem
 {
     ITurtleUpgrade getUpgrade( ItemStack stack, TurtleSide side );
     int getFuelLevel( ItemStack stack );
     ResourceLocation getOverlay( ItemStack stack );
+    int getColour( @Nonnull ItemStack stack );
 }

src/main/java/dan200/computercraft/shared/turtle/items/ItemTurtleBase.java

@@ -22,14 +22,13 @@
 import net.minecraft.item.ItemStack;
 import net.minecraft.tileentity.TileEntity;
 import net.minecraft.util.EnumFacing;
+import net.minecraft.util.NonNullList;
 import net.minecraft.util.ResourceLocation;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
-import java.util.ArrayList;
-import java.util.List;
 
 public abstract class ItemTurtleBase extends ItemComputerBase implements ITurtleItem
 {
@@ -43,9 +42,9 @@ protected ItemTurtleBase( Block block )
     public abstract ItemStack create( int id, String label, int colour, ITurtleUpgrade leftUpgrade, ITurtleUpgrade rightUpgrade, int fuelLevel, ResourceLocation overlay );
 
     @Override
-    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull List<ItemStack> list )
+    public void getSubItems( @Nonnull Item itemID, @Nullable CreativeTabs tabs, @Nonnull NonNullList<ItemStack> list )
     {
-        List<ItemStack> all = new ArrayList<ItemStack>();
+        NonNullList<ItemStack> all = NonNullList.create();
         ComputerCraft.addAllUpgradedTurtles( all );
         for( ItemStack stack : all )
         {
@@ -72,7 +71,7 @@ public boolean placeBlockAt( @Nonnull ItemStack stack, @Nonnull EntityPlayer pla
         return false;
     }
 
-    public void setupTurtleAfterPlacement( ItemStack stack, ITurtleTile turtle )
+    public void setupTurtleAfterPlacement( @Nonnull ItemStack stack, ITurtleTile turtle )
     {
         // Set ID
         int id = getComputerID( stack );
@@ -115,7 +114,7 @@ public void setupTurtleAfterPlacement( ItemStack stack, ITurtleTile turtle )
 
     @Nonnull
     @Override
-    public String getUnlocalizedName( ItemStack stack )
+    public String getUnlocalizedName( @Nonnull ItemStack stack )
     {
         ComputerFamily family = getFamily( stack );
         switch( family )

src/main/java/dan200/computercraft/shared/turtle/items/ItemTurtleLegacy.java

@@ -16,6 +16,8 @@
 import net.minecraft.nbt.NBTTagCompound;
 import net.minecraft.util.ResourceLocation;
 
+import javax.annotation.Nonnull;
+
 public class ItemTurtleLegacy extends ItemTurtleBase
 {
     public ItemTurtleLegacy( Block block )
@@ -81,7 +83,7 @@ public ItemStack create( int id, String label, int colour, ITurtleUpgrade leftUp
     // IComputerItem implementation
 
     @Override
-    public int getComputerID( ItemStack stack )
+    public int getComputerID( @Nonnull ItemStack stack )
     {
         if( stack.hasTagCompound() && stack.getTagCompound().hasKey( "computerID" ) )
         {
@@ -103,7 +105,7 @@ public ComputerFamily getFamily( int damage )
     // ITurtleItem implementation
 
     @Override
-    public ITurtleUpgrade getUpgrade( ItemStack stack, TurtleSide side )
+    public ITurtleUpgrade getUpgrade( @Nonnull ItemStack stack, TurtleSide side )
     {
         int damage = stack.getItemDamage();
         switch( side )
@@ -129,16 +131,16 @@ public ITurtleUpgrade getUpgrade( ItemStack stack, TurtleSide side )
     }
 
     @Override
-    public int getColour( ItemStack stack )
+    public int getColour( @Nonnull ItemStack stack )
     {
         return -1;
     }
 
     @Override
-    public ResourceLocation getOverlay( ItemStack stack ) { return null; }
+    public ResourceLocation getOverlay( @Nonnull ItemStack stack ) { return null; }
 
     @Override
-    public int getFuelLevel( ItemStack stack )
+    public int getFuelLevel( @Nonnull ItemStack stack )
     {
         if( stack.hasTagCompound() )
         {

src/main/java/dan200/computercraft/shared/turtle/items/ItemTurtleNormal.java

@@ -18,6 +18,8 @@
 import net.minecraft.util.ResourceLocation;
 import net.minecraftforge.common.util.Constants;
 
+import javax.annotation.Nonnull;
+
 public class ItemTurtleNormal extends ItemTurtleBase implements IColouredItem
 {
     public ItemTurtleNormal( Block block )
@@ -87,7 +89,7 @@ public ItemStack create( int id, String label, int colour, ITurtleUpgrade leftUp
     // IComputerItem implementation
 
     @Override
-    public int getComputerID( ItemStack stack )
+    public int getComputerID( @Nonnull ItemStack stack )
     {
         if( stack.hasTagCompound() )
         {
@@ -109,7 +111,7 @@ public ComputerFamily getFamily( int damage )
     // ITurtleItem implementation
 
     @Override
-    public ITurtleUpgrade getUpgrade( ItemStack stack, TurtleSide side )
+    public ITurtleUpgrade getUpgrade( @Nonnull ItemStack stack, TurtleSide side )
     {
         if( stack.hasTagCompound() )
         {
@@ -152,14 +154,14 @@ public ITurtleUpgrade getUpgrade( ItemStack stack, TurtleSide side )
     }
 
     @Override
-    public int getColour( ItemStack stack )
+    public int getColour( @Nonnull ItemStack stack )
     {
         NBTTagCompound tag = stack.getTagCompound();
         return tag == null ? -1 : ColourUtils.getHexColour( tag );
     }
 
     @Override
-    public ResourceLocation getOverlay( ItemStack stack )
+    public ResourceLocation getOverlay( @Nonnull ItemStack stack )
     {
         if( stack.hasTagCompound() )
         {
@@ -175,7 +177,7 @@ public ResourceLocation getOverlay( ItemStack stack )
     }
 
     @Override
-    public int getFuelLevel( ItemStack stack )
+    public int getFuelLevel( @Nonnull ItemStack stack )
     {
         if( stack.hasTagCompound() )
         {

src/main/java/dan200/computercraft/shared/turtle/items/TurtleItemFactory.java

@@ -12,15 +12,17 @@
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 import dan200.computercraft.shared.computer.core.IComputer;
 import dan200.computercraft.shared.turtle.blocks.ITurtleTile;
-import dan200.computercraft.shared.util.Colour;
 import dan200.computercraft.shared.util.ReflectionUtil;
 import net.minecraft.block.Block;
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.util.ResourceLocation;
 
+import javax.annotation.Nonnull;
+
 public class TurtleItemFactory
 {
+    @Nonnull
     public static ItemStack create( ITurtleTile turtle )
     {
         ITurtleUpgrade leftUpgrade = turtle.getAccess().getUpgrade( TurtleSide.Left );
@@ -47,6 +49,7 @@ public static ItemStack create( ITurtleTile turtle )
         return create( -1, null, turtle.getColour(), turtle.getFamily(), leftUpgrade, rightUpgrade, 0, turtle.getOverlay() );
     }
 
+    @Nonnull
     public static ItemStack create( int id, String label, int colour, ComputerFamily family, ITurtleUpgrade leftUpgrade, ITurtleUpgrade rightUpgrade, int fuelLevel, ResourceLocation overlay )
     {
         switch( family )
@@ -81,9 +84,9 @@ public static ItemStack create( int id, String label, int colour, ComputerFamily
                     ItemTurtleBase beginnersItem = ((ItemTurtleBase)Item.getItemFromBlock( beginnersBlock ));
                     return beginnersItem.create( id, label, colour, leftUpgrade, rightUpgrade, fuelLevel, overlay );
                 }
-                return null;
+                return ItemStack.EMPTY;
             }
         }
-        return null;
+        return ItemStack.EMPTY;
     }
 }

src/main/java/dan200/computercraft/shared/turtle/recipes/TurtleRecipe.java

@@ -13,7 +13,9 @@
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.item.crafting.IRecipe;
+import net.minecraft.util.NonNullList;
 import net.minecraft.world.World;
+import net.minecraftforge.common.ForgeHooks;
 
 import javax.annotation.Nonnull;
 
@@ -34,6 +36,7 @@ public int getRecipeSize()
         return 9;
     }
     
+    @Nonnull
     @Override
     public ItemStack getRecipeOutput()
     {
@@ -43,9 +46,10 @@ public ItemStack getRecipeOutput()
     @Override
     public boolean matches( @Nonnull InventoryCrafting _inventory, @Nonnull World world )
     {
-        return (getCraftingResult( _inventory ) != null);
+        return !getCraftingResult( _inventory ).isEmpty();
     }
 
+    @Nonnull
     @Override
     public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
     {
@@ -57,7 +61,7 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
             for( int x=0; x<3; ++x )
             {
                 ItemStack item = inventory.getStackInRowAndColumn(x, y);
-                if( item != null && item.getItem() == m_recipe[ x + y*3 ] )
+                if( !item.isEmpty() && item.getItem() == m_recipe[ x + y*3 ] )
                 {
                     if( item.getItem() instanceof IComputerItem )
                     {
@@ -69,13 +73,13 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
                         }
                         else
                         {
-                            return null;
+                            return ItemStack.EMPTY;
                         }
                     }
                 }
                 else
                 {
-                    return null;
+                    return ItemStack.EMPTY;
                 }
             }
         }
@@ -94,13 +98,13 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
 
     @Nonnull
     @Override
-    public ItemStack[] getRemainingItems( @Nonnull InventoryCrafting inventoryCrafting )
+    public NonNullList<ItemStack> getRemainingItems( @Nonnull InventoryCrafting inventoryCrafting )
     {
-        ItemStack[] results = new ItemStack[ inventoryCrafting.getSizeInventory() ];
-        for (int i = 0; i < results.length; ++i)
+        NonNullList<ItemStack> results = NonNullList.withSize( inventoryCrafting.getSizeInventory(), ItemStack.EMPTY );
+        for( int i = 0; i < results.size(); ++i )
         {
-            ItemStack stack = inventoryCrafting.getStackInSlot(i);
-            results[i] = net.minecraftforge.common.ForgeHooks.getContainerItem(stack);
+            ItemStack stack = inventoryCrafting.getStackInSlot( i );
+            results.set( i, ForgeHooks.getContainerItem( stack ) );
         }
         return results;
     }

src/main/java/dan200/computercraft/shared/turtle/recipes/TurtleUpgradeRecipe.java

@@ -17,8 +17,10 @@
 import net.minecraft.inventory.InventoryCrafting;
 import net.minecraft.item.ItemStack;
 import net.minecraft.item.crafting.IRecipe;
+import net.minecraft.util.NonNullList;
 import net.minecraft.util.ResourceLocation;
 import net.minecraft.world.World;
+import net.minecraftforge.common.ForgeHooks;
 
 import javax.annotation.Nonnull;
 
@@ -34,6 +36,7 @@ public int getRecipeSize()
         return 3;
     }
     
+    @Nonnull
     @Override
     public ItemStack getRecipeOutput()
     {
@@ -43,60 +46,61 @@ public ItemStack getRecipeOutput()
     @Override
     public boolean matches( @Nonnull InventoryCrafting inventory, @Nonnull World world )
     {
-        return (getCraftingResult( inventory ) != null);
+        return !getCraftingResult( inventory ).isEmpty();
     }
 
+    @Nonnull
     @Override
     public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
     {
         // Scan the grid for a row containing a turtle and 1 or 2 items
-        ItemStack leftItem = null;
-        ItemStack turtle = null;
-        ItemStack rightItem = null;
+        ItemStack leftItem = ItemStack.EMPTY;
+        ItemStack turtle = ItemStack.EMPTY;
+        ItemStack rightItem = ItemStack.EMPTY;
 
         for( int y=0; y<inventory.getHeight(); ++y )
         {
-            if( turtle == null )
+            if( turtle.isEmpty() )
             {
                 // Search this row for potential turtles
                 boolean finishedRow = false;
                 for( int x=0; x<inventory.getWidth(); ++x )
                 {
                     ItemStack item = inventory.getStackInRowAndColumn(x, y);
-                    if( item != null ) {
+                    if( !item.isEmpty() ) {
                         if( finishedRow ) {
-                            return null;
+                            return ItemStack.EMPTY;
                         }
                         
                         if( item.getItem() instanceof ITurtleItem ) {
                             // Item is a turtle
-                            if( turtle == null ) {
+                            if( turtle.isEmpty() ) {
                                 turtle = item;
                             } else {
-                                return null;
+                                return ItemStack.EMPTY;
                             }
                         } else {
                             // Item is not a turtle
-                            if( turtle == null && leftItem == null ) {
+                            if( turtle.isEmpty() && leftItem.isEmpty() ) {
                                 leftItem = item;
-                            } else if( turtle != null && rightItem == null ) {
+                            } else if( !turtle.isEmpty() && rightItem.isEmpty() ) {
                                 rightItem = item;
                             } else {
-                                return null;
+                                return ItemStack.EMPTY;
                             }
                         }
                     } else {
                         // Item is empty
-                        if( leftItem != null || turtle != null ) {
+                        if( !leftItem.isEmpty() || !turtle.isEmpty() ) {
                             finishedRow = true;
                         }
                     }
                 }
                 
                 // If we found anything, check we found a turtle too
-                if( turtle == null && (leftItem != null || rightItem != null) )
+                if( turtle.isEmpty() && (!leftItem.isEmpty() || !rightItem.isEmpty()) )
                 {
-                    return null;
+                    return ItemStack.EMPTY;
                 }
             }
             else
@@ -105,17 +109,17 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
                 for( int x=0; x<inventory.getWidth(); ++x )
                 {
                     ItemStack item = inventory.getStackInRowAndColumn(x, y);
-                    if( item != null ) {
-                        return null;
+                    if( !item.isEmpty() ) {
+                        return ItemStack.EMPTY;
                     }
                 }
             }
         }
         
         // See if we found a turtle + one or more items
-        if( turtle == null || (leftItem == null && rightItem == null))
+        if( turtle.isEmpty() || (leftItem.isEmpty() && rightItem.isEmpty()) )
         {
-            return null;
+            return ItemStack.EMPTY;
         }
 
         // At this point we have a turtle + 1 or 2 items
@@ -131,20 +135,20 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
         ItemStack[] items = new ItemStack[]{ rightItem, leftItem };
         for( int i=0; i<2; ++i )
         {
-            if( items[i] != null )
+            if( !items[i].isEmpty() )
             {
                 ITurtleUpgrade itemUpgrade = ComputerCraft.getTurtleUpgrade( items[ i ] );
                 if( itemUpgrade == null )
                 {
-                    return null;
+                    return ItemStack.EMPTY;
                 }
                 if( upgrades[i] != null )
                 {
-                    return null;
+                    return ItemStack.EMPTY;
                 }
                 if( !CCTurtleProxyCommon.isUpgradeSuitableForFamily( family, itemUpgrade ) )
                 {
-                    return null;
+                    return ItemStack.EMPTY;
                 }
                 upgrades[i] = itemUpgrade;
             }
@@ -161,13 +165,13 @@ public ItemStack getCraftingResult( @Nonnull InventoryCrafting inventory )
 
     @Nonnull
     @Override
-    public ItemStack[] getRemainingItems( @Nonnull InventoryCrafting inventoryCrafting )
+    public NonNullList<ItemStack> getRemainingItems( @Nonnull InventoryCrafting inventoryCrafting )
     {
-        ItemStack[] results = new ItemStack[ inventoryCrafting.getSizeInventory() ];
-        for (int i = 0; i < results.length; ++i)
+        NonNullList<ItemStack> results = NonNullList.withSize( inventoryCrafting.getSizeInventory(), ItemStack.EMPTY );
+        for( int i = 0; i < results.size(); ++i )
         {
-            ItemStack stack = inventoryCrafting.getStackInSlot(i);
-            results[i] = net.minecraftforge.common.ForgeHooks.getContainerItem(stack);
+            ItemStack stack = inventoryCrafting.getStackInSlot( i );
+            results.set( i, ForgeHooks.getContainerItem( stack ) );
         }
         return results;
     }

src/main/java/dan200/computercraft/shared/turtle/upgrades/TurtleCraftingTable.java

@@ -69,6 +69,7 @@ public TurtleUpgradeType getType()
         return TurtleUpgradeType.Peripheral;
     }
     
+    @Nonnull
     @Override
     public ItemStack getCraftingItem()
     {
@@ -85,7 +86,7 @@ public IPeripheral createPeripheral( @Nonnull ITurtleAccess turtle, @Nonnull Tur
     @Override
     public TurtleCommandResult useTool( @Nonnull ITurtleAccess turtle, @Nonnull TurtleSide side, @Nonnull TurtleVerb verb, @Nonnull EnumFacing dir )
     {
-        return null;
+        return TurtleCommandResult.failure();
     }
 
     @SideOnly( Side.CLIENT )

src/main/java/dan200/computercraft/shared/turtle/upgrades/TurtleInventoryCrafting.java

@@ -13,8 +13,9 @@
 import net.minecraft.inventory.InventoryCrafting;
 import net.minecraft.item.ItemStack;
 import net.minecraft.item.crafting.CraftingManager;
-import net.minecraft.util.text.TextComponentString;
+import net.minecraft.util.NonNullList;
 import net.minecraft.util.text.ITextComponent;
+import net.minecraft.util.text.TextComponentString;
 import net.minecraft.world.World;
 import net.minecraft.world.WorldServer;
 
@@ -35,6 +36,7 @@ public TurtleInventoryCrafting( ITurtleAccess turtle )
         m_yStart = 0;
     }
 
+    @Nonnull
     private ItemStack tryCrafting( int xStart, int yStart )
     {
         m_xStart = xStart;
@@ -48,9 +50,9 @@ private ItemStack tryCrafting( int xStart, int yStart )
                 if( x < m_xStart || x >= m_xStart + 3 ||
                     y < m_yStart || y >= m_yStart + 3 )
                 {
-                    if( m_turtle.getInventory().getStackInSlot( x + y * TileTurtle.INVENTORY_WIDTH ) != null )
+                    if( !m_turtle.getInventory().getStackInSlot( x + y * TileTurtle.INVENTORY_WIDTH ).isEmpty() )
                     {
-                        return null;
+                        return ItemStack.EMPTY;
                     }
                 }
             }
@@ -69,21 +71,21 @@ public ArrayList<ItemStack> doCrafting( World world, int maxCount )
 
         // Find out what we can craft
         ItemStack result = tryCrafting( 0, 0 );
-        if( result == null )
+        if( result.isEmpty() )
         {
             result = tryCrafting( 0, 1 );
         }
-        if( result == null )
+        if( result.isEmpty() )
         {
             result = tryCrafting( 1, 0 );
         }
-        if( result == null )
+        if( result.isEmpty() )
         {
             result = tryCrafting( 1, 1 );
         }
 
         // Craft it
-        if( result != null )
+        if( !result.isEmpty() )
         {
             // Special case: craft(0) just returns an empty list if crafting was possible
             ArrayList<ItemStack> results = new ArrayList<ItemStack>();
@@ -101,17 +103,17 @@ public ArrayList<ItemStack> doCrafting( World world, int maxCount )
                 for( int n=0; n<size; ++n )
                 {
                     ItemStack stack = getStackInSlot( n );
-                    if( stack != null && (minStackSize == 0 || minStackSize > stack.stackSize) )
+                    if( !stack.isEmpty() && (minStackSize == 0 || minStackSize > stack.getCount()) )
                     {
-                        minStackSize = stack.stackSize;
+                        minStackSize = stack.getCount();
                     }
                 }
                 
                 if( minStackSize > 1 )
                 {            
-                    numToCraft = Math.min( minStackSize, result.getMaxStackSize() / result.stackSize );
+                    numToCraft = Math.min( minStackSize, result.getMaxStackSize() / result.getCount() );
                     numToCraft = Math.min( numToCraft, maxCount );
-                    result.stackSize = result.stackSize * numToCraft;
+                    result.setCount( result.getCount() * numToCraft );
                 }
             }
 
@@ -121,21 +123,21 @@ public ArrayList<ItemStack> doCrafting( World world, int maxCount )
             results.add( result );
 
             // Consume resources from the inventory
-            ItemStack[] remainingItems = CraftingManager.getInstance().getRemainingItems( this, world );
+            NonNullList<ItemStack> remainingItems = CraftingManager.getInstance().getRemainingItems( this, world );
             for( int n=0; n<size; ++n )
             {
                 ItemStack stack = getStackInSlot( n );
-                if( stack != null )
+                if( !stack.isEmpty() )
                 {
                     decrStackSize( n, numToCraft );
 
-                    ItemStack replacement = remainingItems[n];
-                    if( replacement != null )
+                    ItemStack replacement = remainingItems.get(n);
+                    if( !replacement.isEmpty() )
                     {
                         if( !(replacement.isItemStackDamageable() && replacement.getItemDamage() >= replacement.getMaxDamage()) )
                         {
-                            replacement.stackSize = Math.min( numToCraft, replacement.getMaxStackSize() );
-                            if( getStackInSlot( n ) == null )
+                            replacement.setCount( Math.min( numToCraft, replacement.getMaxStackSize() ) );
+                            if( getStackInSlot( n ).isEmpty() )
                             {
                                 setInventorySlotContents( n, replacement );
                             }
@@ -153,6 +155,7 @@ public ArrayList<ItemStack> doCrafting( World world, int maxCount )
         return null;
     }
 
+    @Nonnull
     @Override
     public ItemStack getStackInRowAndColumn(int x, int y)
     {
@@ -160,7 +163,7 @@ public ItemStack getStackInRowAndColumn(int x, int y)
         {
             return getStackInSlot( x + y * getWidth() );
         }
-        return null;
+        return ItemStack.EMPTY;
     }
 
     @Override
@@ -195,6 +198,7 @@ public int getSizeInventory()
         return getWidth() * getHeight();
     }
 
+    @Nonnull
     @Override
     public ItemStack getStackInSlot( int i )
     {
@@ -222,6 +226,7 @@ public ITextComponent getDisplayName()
         return new TextComponentString( "" );
     }
 
+    @Nonnull
     @Override
     public ItemStack removeStackFromSlot( int i )
     {
@@ -229,6 +234,7 @@ public ItemStack removeStackFromSlot( int i )
         return m_turtle.getInventory().removeStackFromSlot( i );
     }
 
+    @Nonnull
     @Override
     public ItemStack decrStackSize( int i, int size )
     {
@@ -237,7 +243,7 @@ public ItemStack decrStackSize( int i, int size )
     }
 
     @Override
-    public void setInventorySlotContents( int i, ItemStack stack )
+    public void setInventorySlotContents( int i, @Nonnull ItemStack stack )
     {
         i = modifyIndex( i );
         m_turtle.getInventory().setInventorySlotContents( i, stack );
@@ -256,7 +262,7 @@ public void markDirty()
     }
 
     @Override
-    public boolean isUseableByPlayer( EntityPlayer player )
+    public boolean isUsableByPlayer( EntityPlayer player )
     {
         return true;
     }
@@ -272,7 +278,7 @@ public void closeInventory( EntityPlayer player )
     }
 
     @Override
-    public boolean isItemValidForSlot( int i, ItemStack stack )
+    public boolean isItemValidForSlot( int i, @Nonnull ItemStack stack )
     {
         i = modifyIndex( i );
         return m_turtle.getInventory().isItemValidForSlot( i, stack );
@@ -301,7 +307,7 @@ public void clear()
         for( int i=0; i<getSizeInventory(); ++i )
         {
             int j = modifyIndex( i );
-            m_turtle.getInventory().setInventorySlotContents( j, null );
+            m_turtle.getInventory().setInventorySlotContents( j, ItemStack.EMPTY );
         }
     }
 }

src/main/java/dan200/computercraft/shared/turtle/upgrades/TurtleModem.java

@@ -130,6 +130,7 @@ public TurtleUpgradeType getType()
         return TurtleUpgradeType.Peripheral;
     }
     
+    @Nonnull
     @Override
     public ItemStack getCraftingItem()
     {
@@ -153,7 +154,7 @@ public IPeripheral createPeripheral( @Nonnull ITurtleAccess turtle, @Nonnull Tur
     @Override
     public TurtleCommandResult useTool( @Nonnull ITurtleAccess turtle, @Nonnull TurtleSide side, @Nonnull TurtleVerb verb, @Nonnull EnumFacing dir )
     {
-        return null;
+        return TurtleCommandResult.failure();
     }
 
     @SideOnly( Side.CLIENT )

src/main/java/dan200/computercraft/shared/turtle/upgrades/TurtleSpeaker.java

@@ -114,6 +114,7 @@ public TurtleUpgradeType getType()
         return TurtleUpgradeType.Peripheral;
     }
 
+    @Nonnull
     @Override
     public ItemStack getCraftingItem()
     {

src/main/java/dan200/computercraft/shared/turtle/upgrades/TurtleTool.java

@@ -88,6 +88,7 @@ public TurtleUpgradeType getType()
         return TurtleUpgradeType.Tool;
     }
 
+    @Nonnull
     @Override
     public ItemStack getCraftingItem()
     {
@@ -187,10 +188,10 @@ private TurtleCommandResult attack( final ITurtleAccess turtle, EnumFacing direc
             ComputerCraft.setEntityDropConsumer( hitEntity, new IEntityDropConsumer()
             {
                 @Override
-                public void consumeDrop( Entity entity, ItemStack drop )
+                public void consumeDrop( Entity entity, @Nonnull ItemStack drop )
                 {
                     ItemStack remainder = InventoryUtil.storeItems( drop, turtle.getItemHandler(), turtle.getSelectedSlot() );
-                    if( remainder != null )
+                    if( !remainder.isEmpty() )
                     {
                         WorldUtil.dropItemStack( remainder, world, position, turtle.getDirection().getOpposite() );
                     }
@@ -283,7 +284,7 @@ private TurtleCommandResult dig( ITurtleAccess turtle, EnumFacing direction )
                     for( ItemStack stack : items )
                     {
                         ItemStack remainder = InventoryUtil.storeItems( stack, turtle.getItemHandler(), turtle.getSelectedSlot() );
-                        if( remainder != null )
+                        if( !remainder.isEmpty() )
                         {
                             // If there's no room for the items, drop them
                             WorldUtil.dropItemStack( remainder, world, position, direction );

src/main/java/dan200/computercraft/shared/util/CreativeTabMain.java

@@ -8,7 +8,7 @@
 
 import dan200.computercraft.ComputerCraft;
 import net.minecraft.creativetab.CreativeTabs;
-import net.minecraft.item.Item;
+import net.minecraft.item.ItemStack;
 
 import javax.annotation.Nonnull;
 
@@ -21,9 +21,9 @@ public CreativeTabMain( int i )
     
     @Nonnull
     @Override
-    public Item getTabIconItem()
+    public ItemStack getTabIconItem()
     {
-        return Item.getItemFromBlock( ComputerCraft.Blocks.computer );
+        return new ItemStack( ComputerCraft.Blocks.computer );
     }
     
     @Nonnull

src/main/java/dan200/computercraft/shared/util/CreativeTabTreasure.java

@@ -8,7 +8,7 @@
 
 import dan200.computercraft.ComputerCraft;
 import net.minecraft.creativetab.CreativeTabs;
-import net.minecraft.item.Item;
+import net.minecraft.item.ItemStack;
 
 import javax.annotation.Nonnull;
 
@@ -21,9 +21,9 @@ public CreativeTabTreasure( int i )
     
     @Nonnull
     @Override
-    public Item getTabIconItem()
+    public ItemStack getTabIconItem()
     {
-        return ComputerCraft.Items.treasureDisk;
+        return new ItemStack( ComputerCraft.Items.treasureDisk );
     }
     
     @Nonnull

src/main/java/dan200/computercraft/shared/util/DirectionUtil.java

@@ -88,7 +88,7 @@ else if( dir == EnumFacing.UP )
 
     public static EnumFacing fromEntityRot( EntityLivingBase player )
     {
-        int rot = MathHelper.floor_float( ( player.rotationYaw / 90.0f ) + 0.5f ) & 0x3;
+        int rot = MathHelper.floor( ( player.rotationYaw / 90.0f ) + 0.5f ) & 0x3;
         switch( rot ) {
             case 0: return EnumFacing.NORTH;
             case 1: return EnumFacing.EAST;

src/main/java/dan200/computercraft/shared/util/IEntityDropConsumer.java

@@ -8,7 +8,9 @@
 import net.minecraft.entity.Entity;
 import net.minecraft.item.ItemStack;
 
+import javax.annotation.Nonnull;
+
 public interface IEntityDropConsumer
 {
-    void consumeDrop( Entity dropper, ItemStack drop );
+    void consumeDrop( Entity dropper, @Nonnull ItemStack drop );
 }

src/main/java/dan200/computercraft/shared/util/ImpostorRecipe.java

@@ -14,7 +14,7 @@
 
 public class ImpostorRecipe extends ShapedRecipes
 {
-    public ImpostorRecipe( int width, int height, ItemStack[] ingredients, ItemStack result )
+    public ImpostorRecipe( int width, int height, ItemStack[] ingredients, @Nonnull ItemStack result )
     {
         super( width, height, ingredients, result );
     }
@@ -25,9 +25,10 @@ public boolean matches( @Nonnull InventoryCrafting inv, World world )
         return false;
     }
     
+    @Nonnull
     @Override
     public ItemStack getCraftingResult( @Nonnull InventoryCrafting _inventory )
     {
-        return null;
+        return ItemStack.EMPTY;
     }
 }

src/main/java/dan200/computercraft/shared/util/ImpostorShapelessRecipe.java

@@ -11,12 +11,13 @@
 import net.minecraft.item.crafting.ShapelessRecipes;
 import net.minecraft.world.World;
 
+import javax.annotation.Nonnull;
 import java.util.ArrayList;
 import java.util.Arrays;
 
 public class ImpostorShapelessRecipe extends ShapelessRecipes
 {
-    public ImpostorShapelessRecipe( ItemStack result, ItemStack[] ingredients )
+    public ImpostorShapelessRecipe( @Nonnull ItemStack result, ItemStack[] ingredients )
     {
         super( result, new ArrayList<ItemStack>(Arrays.asList( ingredients )));
     }
@@ -27,9 +28,10 @@ public boolean matches( InventoryCrafting inv, World world )
         return false;
     }
 
+    @Nonnull
     @Override
     public ItemStack getCraftingResult( InventoryCrafting _inventory )
     {
-        return null;
+        return ItemStack.EMPTY;
     }
 }

src/main/java/dan200/computercraft/shared/util/InventoryUtil.java

@@ -22,27 +22,26 @@
 import net.minecraftforge.items.wrapper.SidedInvWrapper;
 import org.apache.commons.lang3.tuple.Pair;
 
+import javax.annotation.Nonnull;
+
 public class InventoryUtil
 {
     // Methods for comparing things:
 
-    public static boolean areItemsEqual( ItemStack a, ItemStack b )
+    public static boolean areItemsEqual( @Nonnull ItemStack a, @Nonnull ItemStack b )
     {
         return a == b || ItemStack.areItemStacksEqual( a, b );
     }
 
-    public static boolean areItemsStackable( ItemStack a, ItemStack b )
+    public static boolean areItemsStackable( @Nonnull ItemStack a, @Nonnull ItemStack b )
     {
         return a == b || ItemHandlerHelper.canItemStacksStack( a, b );
     }
 
-    public static ItemStack copyItem( ItemStack a )
+    @Nonnull
+    public static ItemStack copyItem( @Nonnull ItemStack a )
     {
-        if( a != null )
-        {
-            return a.copy();
-        }
-        return null;
+        return a.copy();
     }
 
     // Methods for finding inventories:
@@ -96,19 +95,22 @@ else if( tileEntity instanceof IInventory )
 
     // Methods for placing into inventories:
 
-    public static ItemStack storeItems( ItemStack itemstack, IItemHandler inventory, int start, int range, int begin )
+    @Nonnull
+    public static ItemStack storeItems( @Nonnull ItemStack itemstack, IItemHandler inventory, int start, int range, int begin )
     {
         int[] slots = makeSlotList( start, range, begin );
         return storeItems( itemstack, inventory, slots );
     }
 
-    public static ItemStack storeItems( ItemStack itemstack, IItemHandler inventory, int begin )
+    @Nonnull
+    public static ItemStack storeItems( @Nonnull ItemStack itemstack, IItemHandler inventory, int begin )
     {
         int[] slots = makeSlotList( 0, inventory.getSlots(), begin );
         return storeItems( itemstack, inventory, slots );
     }
 
-    public static ItemStack storeItems( ItemStack itemstack, IItemHandler inventory )
+    @Nonnull
+    public static ItemStack storeItems( @Nonnull ItemStack itemstack, IItemHandler inventory )
     {
         int[] slots = makeSlotList( 0, inventory.getSlots(), 0 ); // TODO: optimise this out?
         return storeItems( itemstack, inventory, slots );
@@ -116,18 +118,21 @@ public static ItemStack storeItems( ItemStack itemstack, IItemHandler inventory
 
     // Methods for taking out of inventories
 
+    @Nonnull
     public static ItemStack takeItems( int count, IItemHandler inventory, int start, int range, int begin )
     {
         int[] slots = makeSlotList( start, range, begin );
         return takeItems( count, inventory, slots );
     }
 
+    @Nonnull
     public static ItemStack takeItems( int count, IItemHandler inventory, int begin )
     {
         int[] slots = makeSlotList( 0, inventory.getSlots(), begin );
         return takeItems( count, inventory, slots );
     }
 
+    @Nonnull
     public static ItemStack takeItems( int count, IItemHandler inventory )
     {
         int[] slots = makeSlotList( 0, inventory.getSlots(), 0 );
@@ -151,57 +156,59 @@ private static int[] makeSlotList( int start, int range, int begin )
         return slots;
     }
 
-    private static ItemStack storeItems( ItemStack stack, IItemHandler inventory, int[] slots )
+    @Nonnull
+    private static ItemStack storeItems( @Nonnull ItemStack stack, IItemHandler inventory, int[] slots )
     {
         if( slots == null || slots.length == 0 )
         {
             return stack;
         }
-        if( stack == null || stack.stackSize == 0 )
+        if( stack.isEmpty() )
         {
-            return null;
+            return ItemStack.EMPTY;
         }
 
         // Inspect the slots in order and try to find empty or stackable slots
         ItemStack remainder = stack.copy();
         for( int slot : slots )
         {
-            if( remainder == null ) break;
+            if( remainder.isEmpty() ) break;
             remainder = inventory.insertItem( slot, remainder, false );
         }
         return areItemsEqual( stack, remainder ) ? stack : remainder;
     }
 
+    @Nonnull
     private static ItemStack takeItems( int count, IItemHandler inventory, int[] slots )
     {
         if( slots == null )
         {
-            return null;
+            return ItemStack.EMPTY;
         }
 
         // Combine multiple stacks from inventory into one if necessary
-        ItemStack partialStack = null;
+        ItemStack partialStack = ItemStack.EMPTY;
         int countRemaining = count;
         for( int slot : slots )
         {
             if( countRemaining <= 0 ) break;
 
             ItemStack stack = inventory.getStackInSlot( slot );
-            if( stack != null )
+            if( !stack.isEmpty() )
             {
-                if( partialStack == null || areItemsStackable( stack, partialStack ) )
+                if( partialStack.isEmpty() || areItemsStackable( stack, partialStack ) )
                 {
                     ItemStack extracted = inventory.extractItem( slot, countRemaining, false );
-                    if( extracted != null )
+                    if( !extracted.isEmpty() )
                     {
-                        countRemaining -= extracted.stackSize;
-                        if( partialStack == null )
+                        countRemaining -= extracted.getCount();
+                        if( partialStack.isEmpty() )
                         {
                             partialStack = extracted;
                         }
                         else
                         {
-                            partialStack.stackSize += extracted.stackSize;
+                            partialStack.grow( extracted.getCount() );
                         }
                     }
                 }

src/main/java/dan200/computercraft/shared/util/RedstoneUtil.java

@@ -76,7 +76,7 @@ public static void propogateRedstoneOutput( World world, BlockPos pos, EnumFacin
         IBlockState neighbour = world.getBlockState( neighbourPos );
         if( neighbour.getBlock() != Blocks.AIR )
         {
-            world.notifyBlockOfStateChange( neighbourPos, block.getBlock() );
+            world.neighborChanged( neighbourPos, block.getBlock(), pos );
             if( neighbour.getBlock().isNormalCube( neighbour, world, neighbourPos ) )
             {
                 world.notifyNeighborsOfStateExcept( neighbourPos, neighbour.getBlock(), side.getOpposite() );

src/main/java/dan200/computercraft/shared/util/WorldUtil.java

@@ -14,6 +14,7 @@
 import net.minecraft.world.World;
 import org.apache.commons.lang3.tuple.Pair;
 
+import javax.annotation.Nonnull;
 import java.util.List;
 
 public class WorldUtil
@@ -112,12 +113,12 @@ else if( littleBox.intersectsWith( bigBox ) )
         return null;
     }
 
-    public static void dropItemStack( ItemStack stack, World world, BlockPos pos )
+    public static void dropItemStack( @Nonnull ItemStack stack, World world, BlockPos pos )
     {
         dropItemStack( stack, world, pos, null );
     }
 
-    public static void dropItemStack( ItemStack stack, World world, BlockPos pos, EnumFacing direction )
+    public static void dropItemStack( @Nonnull ItemStack stack, World world, BlockPos pos, EnumFacing direction )
     {
         double xDir;
         double yDir;
@@ -141,18 +142,18 @@ public static void dropItemStack( ItemStack stack, World world, BlockPos pos, En
         dropItemStack( stack, world, xPos, yPos, zPos, xDir, yDir, zDir );
     }
 
-    public static void dropItemStack( ItemStack stack, World world, double xPos, double yPos, double zPos )
+    public static void dropItemStack( @Nonnull ItemStack stack, World world, double xPos, double yPos, double zPos )
     {
         dropItemStack( stack, world, xPos, yPos, zPos, 0.0, 0.0, 0.0 );
     }
 
-    public static void dropItemStack( ItemStack stack, World world, double xPos, double yPos, double zPos, double xDir, double yDir, double zDir )
+    public static void dropItemStack( @Nonnull ItemStack stack, World world, double xPos, double yPos, double zPos, double xDir, double yDir, double zDir )
     {
         EntityItem entityItem = new EntityItem( world, xPos, yPos, zPos, stack.copy() );
         entityItem.motionX = xDir * 0.7 + world.rand.nextFloat() * 0.2 - 0.1;
         entityItem.motionY = yDir * 0.7 + world.rand.nextFloat() * 0.2 - 0.1;
         entityItem.motionZ = zDir * 0.7 + world.rand.nextFloat() * 0.2 - 0.1;
         entityItem.setDefaultPickupDelay();
-        world.spawnEntityInWorld( entityItem );
+        world.spawnEntity( entityItem );
     }
 }

src/main/resources/mcmod.info

@@ -1,6 +1,6 @@
 [
     {
-        "modid" : "ComputerCraft",
+        "modid" : "computercraft",
         "name" : "ComputerCraft",
         "version" : "${version}",
         "mcversion" : "${mcversion}",