Make the main mod non-null by default

This was actually much more work than I thought it would be. Tests pass,
but I'm sure there's some regressions in here.

build.gradle.kts

@@ -152,7 +152,9 @@ configurations {
 
 dependencies {
     minecraft("net.minecraftforge:forge:$mcVersion-${libs.versions.forge.get()}")
-    annotationProcessor("org.spongepowered:mixin:0.8.5:processor")
+    annotationProcessor("org.spongepowered:mixin:0.8.5-SQUID:processor")
+
+    errorprone(project(":lints"))
 
     compileOnly(libs.jetbrainsAnnotations)
     annotationProcessorEverywhere(libs.autoService)

buildSrc/src/main/kotlin/cc-tweaked.errorprone.gradle.kts

@@ -1,45 +0,0 @@
-import net.ltgt.gradle.errorprone.CheckSeverity
-import net.ltgt.gradle.errorprone.errorprone
-
-plugins {
-    java
-    id("net.ltgt.errorprone")
-}
-
-
-dependencies {
-    val libs = project.extensions.getByType<VersionCatalogsExtension>().named("libs")
-    errorprone(libs.findLibrary("errorProne-core").get())
-    errorprone(libs.findLibrary("nullAway").get())
-}
-
-// Configure default JavaCompile tasks with our arguments.
-sourceSets.all {
-    tasks.named(compileJavaTaskName, JavaCompile::class.java) {
-        options.errorprone {
-            check("InvalidBlockTag", CheckSeverity.OFF) // Broken by @cc.xyz
-            check("InvalidParam", CheckSeverity.OFF) // Broken by records.
-            check("InlineMeSuggester", CheckSeverity.OFF) // Minecraft uses @Deprecated liberally
-            // Too many false positives right now. Maybe we need an indirection for it later on.
-            check("ReferenceEquality",CheckSeverity.OFF)
-            check("UnusedVariable", CheckSeverity.OFF) // Too many false positives with records.
-            check("OperatorPrecedence", CheckSeverity.OFF) // For now.
-            check("AlreadyChecked", CheckSeverity.OFF) // Seems to be broken?
-            check("NonOverridingEquals", CheckSeverity.OFF) // Peripheral.equals makes this hard to avoid
-            check("FutureReturnValueIgnored", CheckSeverity.OFF) // Too many false positives with Netty
-
-            check("NullAway", CheckSeverity.ERROR)
-            option("NullAway:AnnotatedPackages", listOf("dan200.computercraft").joinToString(","))
-            option("NullAway:ExcludedFieldAnnotations", listOf("org.spongepowered.asm.mixin.Shadow").joinToString(","))
-            option("NullAway:CastToNonNullMethod", "dan200.computercraft.core.util.Nullability.assertNonNull")
-            option("NullAway:CheckOptionalEmptiness")
-            option("NullAway:AcknowledgeRestrictiveAnnotations")
-        }
-    }
-}
-
-tasks.compileTestJava {
-    options.errorprone {
-        check("NullAway", CheckSeverity.OFF)
-    }
-}

buildSrc/src/main/kotlin/cc-tweaked.forge.gradle.kts

@@ -7,7 +7,6 @@ import cc.tweaked.gradle.MinecraftConfigurations
 
 plugins {
     id("cc-tweaked.java-convention")
-    id("cc-tweaked.errorprone")
     id("net.minecraftforge.gradle")
     id("org.parchmentmc.librarian.forgegradle")
 }

buildSrc/src/main/kotlin/cc-tweaked.java-convention.gradle.kts

@@ -2,6 +2,8 @@ import cc.tweaked.gradle.CCTweakedPlugin
 import cc.tweaked.gradle.LicenseHeader
 import com.diffplug.gradle.spotless.FormatExtension
 import com.diffplug.spotless.LineEnding
+import net.ltgt.gradle.errorprone.CheckSeverity
+import net.ltgt.gradle.errorprone.errorprone
 import java.nio.charset.StandardCharsets
 
 plugins {
@@ -10,6 +12,7 @@ plugins {
     jacoco
     checkstyle
     id("com.diffplug.spotless")
+    id("net.ltgt.errorprone")
 }
 
 val modVersion: String by extra
@@ -43,6 +46,8 @@ repositories {
             includeGroup("commoble.morered")
             includeGroup("maven.modrinth")
             includeGroup("mezz.jei")
+            // Until https://github.com/SpongePowered/Mixin/pull/593 is merged
+            includeModule("org.spongepowered", "mixin")
         }
     }
 }
@@ -50,6 +55,9 @@ repositories {
 dependencies {
     val libs = project.extensions.getByType<VersionCatalogsExtension>().named("libs")
     checkstyle(libs.findLibrary("checkstyle").get())
+
+    errorprone(libs.findLibrary("errorProne-core").get())
+    errorprone(libs.findLibrary("nullAway").get())
 }
 
 // Configure default JavaCompile tasks with our arguments.
@@ -57,9 +65,36 @@ sourceSets.all {
     tasks.named(compileJavaTaskName, JavaCompile::class.java) {
         // Processing just gives us "No processor claimed any of these annotations", so skip that!
         options.compilerArgs.addAll(listOf("-Xlint", "-Xlint:-processing"))
+
+        options.errorprone {
+            check("InvalidBlockTag", CheckSeverity.OFF) // Broken by @cc.xyz
+            check("InvalidParam", CheckSeverity.OFF) // Broken by records.
+            check("InlineMeSuggester", CheckSeverity.OFF) // Minecraft uses @Deprecated liberally
+            // Too many false positives right now. Maybe we need an indirection for it later on.
+            check("ReferenceEquality", CheckSeverity.OFF)
+            check("UnusedVariable", CheckSeverity.OFF) // Too many false positives with records.
+            check("OperatorPrecedence", CheckSeverity.OFF) // For now.
+            check("AlreadyChecked", CheckSeverity.OFF) // Seems to be broken?
+            check("NonOverridingEquals", CheckSeverity.OFF) // Peripheral.equals makes this hard to avoid
+            check("FutureReturnValueIgnored", CheckSeverity.OFF) // Too many false positives with Netty
+
+            check("NullAway", CheckSeverity.ERROR)
+            option("NullAway:AnnotatedPackages", listOf("dan200.computercraft").joinToString(","))
+            option("NullAway:ExcludedFieldAnnotations", listOf("org.spongepowered.asm.mixin.Shadow").joinToString(","))
+            option("NullAway:CastToNonNullMethod", "dan200.computercraft.core.util.Nullability.assertNonNull")
+            option("NullAway:CheckOptionalEmptiness")
+            option("NullAway:AcknowledgeRestrictiveAnnotations")
+        }
     }
 }
 
+tasks.compileTestJava {
+    options.errorprone {
+        check("NullAway", CheckSeverity.OFF)
+    }
+}
+
+
 tasks.withType(JavaCompile::class.java).configureEach {
     options.encoding = "UTF-8"
 }

buildSrc/src/main/kotlin/cc-tweaked.vanilla.gradle.kts

@@ -6,7 +6,6 @@ import cc.tweaked.gradle.MinecraftConfigurations
 
 plugins {
     id("cc-tweaked.java-convention")
-    id("cc-tweaked.errorprone")
     id("org.spongepowered.gradle.vanilla")
 }
 

projects/common-api/src/main/java/dan200/computercraft/api/turtle/ITurtleAccess.java

@@ -292,7 +292,7 @@ public interface ITurtleAccess {
      * @return The upgrade-specific data.
      * @see #updateUpgradeNBTData(TurtleSide)
      */
-    CompoundTag getUpgradeNBTData(@Nullable TurtleSide side);
+    CompoundTag getUpgradeNBTData(TurtleSide side);
 
     /**
      * Mark the upgrade-specific data as dirty on a specific side. This is required for the data to be synced to the

projects/core-api/build.gradle.kts

@@ -1,7 +1,6 @@
 plugins {
     id("cc-tweaked.java-convention")
     id("cc-tweaked.publishing")
-    id("cc-tweaked.errorprone")
     id("cc-tweaked")
 }
 

projects/core/build.gradle.kts

@@ -5,7 +5,6 @@ plugins {
     id("cc-tweaked.kotlin-convention")
     id("cc-tweaked.java-convention")
     id("cc-tweaked.publishing")
-    id("cc-tweaked.errorprone")
     id("cc-tweaked")
 }
 

projects/lints/build.gradle.kts

@@ -0,0 +1,34 @@
+plugins {
+    id("cc-tweaked.kotlin-convention")
+    id("cc-tweaked.java-convention")
+}
+
+repositories {
+    maven("https://maven.minecraftforge.net") {
+        content {
+            includeGroup("net.minecraftforge")
+            includeGroup("cpw.mods")
+        }
+    }
+}
+
+dependencies {
+    implementation(libs.kotlin.stdlib)
+    implementation(libs.errorProne.api)
+    implementation(libs.nullAway)
+}
+
+tasks.test {
+    jvmArgs(
+        "--add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED",
+        "--add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED",
+        "--add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED",
+        "--add-exports=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED",
+        "--add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED",
+        "--add-exports=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED",
+        "--add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED",
+        "--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED",
+        "--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED",
+        "--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED",
+    )
+}

projects/lints/src/main/kotlin/cc/tweaked/linter/MinecraftLibraryModel.kt

@@ -0,0 +1,38 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2022. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+package cc.tweaked.linter
+
+import com.google.common.collect.ImmutableSet
+import com.google.common.collect.ImmutableSetMultimap
+import com.uber.nullaway.LibraryModels
+import com.uber.nullaway.LibraryModels.MethodRef.methodRef
+
+/**
+ * Extends NullAway's model of Minecraft's code with a couple of extra annotations.
+ */
+class MinecraftLibraryModel : LibraryModels {
+    override fun failIfNullParameters(): ImmutableSetMultimap<LibraryModels.MethodRef, Int> = ImmutableSetMultimap.of()
+    override fun explicitlyNullableParameters(): ImmutableSetMultimap<LibraryModels.MethodRef, Int> =
+        ImmutableSetMultimap.of()
+
+    override fun nonNullParameters(): ImmutableSetMultimap<LibraryModels.MethodRef, Int> = ImmutableSetMultimap.of()
+    override fun nullImpliesTrueParameters(): ImmutableSetMultimap<LibraryModels.MethodRef, Int> =
+        ImmutableSetMultimap.of()
+
+    override fun nullImpliesFalseParameters(): ImmutableSetMultimap<LibraryModels.MethodRef, Int> =
+        ImmutableSetMultimap.of()
+
+    override fun nullImpliesNullParameters(): ImmutableSetMultimap<LibraryModels.MethodRef, Int> =
+        ImmutableSetMultimap.of()
+
+    override fun castToNonNullMethods(): ImmutableSetMultimap<LibraryModels.MethodRef, Int> = ImmutableSetMultimap.of()
+    override fun nullableReturns(): ImmutableSet<LibraryModels.MethodRef> = ImmutableSet.of()
+
+    override fun nonNullReturns(): ImmutableSet<LibraryModels.MethodRef> = ImmutableSet.of(
+        // Reasoning about nullability of BlockEntity.getLevel() is awkward. For now, assume it's non-null.
+        methodRef("net.minecraft.world.level.block.entity.BlockEntity", "getLevel()"),
+    )
+}

projects/lints/src/main/resources/META-INF/services/com.uber.nullaway.LibraryModels

@@ -0,0 +1 @@
+cc.tweaked.linter.MinecraftLibraryModel

settings.gradle.kts

@@ -24,6 +24,7 @@ include(":forge-stubs")
 include(":common-api")
 include(":forge-api")
 
+include(":lints")
 include(":web")
 
 for (project in rootProject.children) {

src/main/java/dan200/computercraft/ComputerCraftAPIImpl.java

@@ -51,7 +51,7 @@ import net.minecraftforge.fluids.FluidStack;
 import net.minecraftforge.fml.ModList;
 import net.minecraftforge.server.ServerLifecycleHooks;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
@@ -64,9 +64,9 @@ public final class ComputerCraftAPIImpl implements ComputerCraftAPIForgeService
     private final DetailRegistry<BlockReference> blockDetails = new DetailRegistryImpl<>(BlockData::fillBasic);
     private final DetailRegistry<FluidStack> fluidStackDetails = new DetailRegistryImpl<>(FluidData::fillBasic);
 
-    private String version;
+    private @Nullable String version;
 
-    public static InputStream getResourceFile(MinecraftServer server, String domain, String subPath) {
+    public static @Nullable InputStream getResourceFile(MinecraftServer server, String domain, String subPath) {
         var manager = server.getResourceManager();
         var resource = manager.getResource(new ResourceLocation(domain, subPath)).orElse(null);
         if (resource == null) return null;
@@ -77,7 +77,6 @@ public final class ComputerCraftAPIImpl implements ComputerCraftAPIForgeService
         }
     }
 
-    @Nonnull
     @Override
     public String getInstalledVersion() {
         if (version != null) return version;
@@ -87,71 +86,75 @@ public final class ComputerCraftAPIImpl implements ComputerCraftAPIForgeService
     }
 
     @Override
-    public int createUniqueNumberedSaveDir(@Nonnull Level world, @Nonnull String parentSubPath) {
+    public int createUniqueNumberedSaveDir(Level world, String parentSubPath) {
-        return ServerContext.get(world.getServer()).getNextId(parentSubPath);
+        var server = world.getServer();
+        if (server == null) throw new IllegalArgumentException("Cannot find server from provided level");
+        return ServerContext.get(server).getNextId(parentSubPath);
     }
 
     @Override
-    public IWritableMount createSaveDirMount(@Nonnull Level world, @Nonnull String subPath, long capacity) {
+    public @Nullable IWritableMount createSaveDirMount(Level world, String subPath, long capacity) {
+        var server = world.getServer();
+        if (server == null) throw new IllegalArgumentException("Cannot find server from provided level");
+
         try {
-            return new FileMount(new File(ServerContext.get(world.getServer()).storageDir().toFile(), subPath), capacity);
+            return new FileMount(new File(ServerContext.get(server).storageDir().toFile(), subPath), capacity);
         } catch (Exception e) {
             return null;
         }
     }
 
     @Override
-    public IMount createResourceMount(@Nonnull String domain, @Nonnull String subPath) {
+    public @Nullable IMount createResourceMount(String domain, String subPath) {
         var manager = ServerLifecycleHooks.getCurrentServer().getResourceManager();
         var mount = ResourceMount.get(domain, subPath, manager);
         return mount.exists("") ? mount : null;
     }
 
     @Override
-    public void registerPeripheralProvider(@Nonnull IPeripheralProvider provider) {
+    public void registerPeripheralProvider(IPeripheralProvider provider) {
         Peripherals.register(provider);
     }
 
     @Override
-    public void registerGenericSource(@Nonnull GenericSource source) {
+    public void registerGenericSource(GenericSource source) {
         GenericMethod.register(source);
     }
 
     @Override
-    public void registerGenericCapability(@Nonnull Capability<?> capability) {
+    public void registerGenericCapability(Capability<?> capability) {
         GenericPeripheralProvider.addCapability(capability);
     }
 
     @Override
-    public void registerBundledRedstoneProvider(@Nonnull IBundledRedstoneProvider provider) {
+    public void registerBundledRedstoneProvider(IBundledRedstoneProvider provider) {
         BundledRedstone.register(provider);
     }
 
     @Override
-    public int getBundledRedstoneOutput(@Nonnull Level world, @Nonnull BlockPos pos, @Nonnull Direction side) {
+    public int getBundledRedstoneOutput(Level world, BlockPos pos, Direction side) {
         return BundledRedstone.getDefaultOutput(world, pos, side);
     }
 
     @Override
-    public void registerMediaProvider(@Nonnull IMediaProvider provider) {
+    public void registerMediaProvider(IMediaProvider provider) {
         MediaProviders.register(provider);
     }
 
-    @Nonnull
     @Override
     public IPacketNetwork getWirelessNetwork() {
         return WirelessNetwork.getUniversal();
     }
 
     @Override
-    public void registerAPIFactory(@Nonnull ILuaAPIFactory factory) {
+    public void registerAPIFactory(ILuaAPIFactory factory) {
         ApiFactories.register(factory);
     }
 
     @Override
     @Deprecated
     @SuppressWarnings("unchecked")
-    public <T> void registerDetailProvider(@Nonnull Class<T> type, @Nonnull IDetailProvider<T> provider) {
+    public <T> void registerDetailProvider(Class<T> type, IDetailProvider<T> provider) {
         if (type == ItemStack.class) {
             itemStackDetails.addProvider((IDetailProvider<ItemStack>) provider);
         } else if (type == BlockReference.class) {
@@ -163,21 +166,19 @@ public final class ComputerCraftAPIImpl implements ComputerCraftAPIForgeService
         }
     }
 
-    @Nonnull
     @Override
-    public IWiredNode createWiredNodeForElement(@Nonnull IWiredElement element) {
+    public IWiredNode createWiredNodeForElement(IWiredElement element) {
         return new WiredNode(element);
     }
 
-    @Nonnull
     @Override
-    public LazyOptional<IWiredElement> getWiredElementAt(@Nonnull BlockGetter world, @Nonnull BlockPos pos, @Nonnull Direction side) {
+    public LazyOptional<IWiredElement> getWiredElementAt(BlockGetter world, BlockPos pos, Direction side) {
         var tile = world.getBlockEntity(pos);
         return tile == null ? LazyOptional.empty() : tile.getCapability(CAPABILITY_WIRED_ELEMENT, side);
     }
 
     @Override
-    public void registerRefuelHandler(@Nonnull TurtleRefuelHandler handler) {
+    public void registerRefuelHandler(TurtleRefuelHandler handler) {
         TurtleRefuelHandlers.register(handler);
     }
 

src/main/java/dan200/computercraft/client/ComputerCraftAPIClientImpl.java

@@ -12,12 +12,11 @@ import dan200.computercraft.api.turtle.TurtleUpgradeSerialiser;
 import dan200.computercraft.client.turtle.TurtleUpgradeModellers;
 import dan200.computercraft.impl.client.ComputerCraftAPIClientService;
 
-import javax.annotation.Nonnull;
 
 @AutoService(ComputerCraftAPIClientService.class)
 public final class ComputerCraftAPIClientImpl implements ComputerCraftAPIClientService {
     @Override
-    public <T extends ITurtleUpgrade> void registerTurtleUpgradeModeller(@Nonnull TurtleUpgradeSerialiser<T> serialiser, @Nonnull TurtleUpgradeModeller<T> modeller) {
+    public <T extends ITurtleUpgrade> void registerTurtleUpgradeModeller(TurtleUpgradeSerialiser<T> serialiser, TurtleUpgradeModeller<T> modeller) {
         TurtleUpgradeModellers.register(serialiser, modeller);
     }
 }

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

@@ -26,7 +26,6 @@ import net.minecraft.world.entity.player.Inventory;
 import net.minecraft.world.item.ItemStack;
 import org.lwjgl.glfw.GLFW;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.io.IOException;
 import java.nio.ByteBuffer;
@@ -37,13 +36,15 @@ import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 
+import static dan200.computercraft.core.util.Nullability.assertNonNull;
+
 public abstract class ComputerScreenBase<T extends ContainerComputerBase> extends AbstractContainerScreen<T> {
     private static final Component OK = Component.translatable("gui.ok");
     private static final Component NO_RESPONSE_TITLE = Component.translatable("gui.computercraft.upload.no_response");
     private static final Component NO_RESPONSE_MSG = Component.translatable("gui.computercraft.upload.no_response.msg",
         Component.literal("import").withStyle(ChatFormatting.DARK_GRAY));
 
-    protected WidgetTerminal terminal;
+    protected @Nullable WidgetTerminal terminal;
     protected Terminal terminalData;
     protected final ComputerFamily family;
     protected final InputHandler input;
@@ -64,6 +65,11 @@ public abstract class ComputerScreenBase<T extends ContainerComputerBase> extend
 
     protected abstract WidgetTerminal createTerminal();
 
+    protected final WidgetTerminal getTerminal() {
+        if (terminal == null) throw new IllegalStateException("Screen has not been initialised yet");
+        return terminal;
+    }
+
     @Override
     protected void init() {
         super.init();
@@ -83,7 +89,7 @@ public abstract class ComputerScreenBase<T extends ContainerComputerBase> extend
     @Override
     public void containerTick() {
         super.containerTick();
-        terminal.update();
+        getTerminal().update();
 
         if (uploadNagDeadline != Long.MAX_VALUE && Util.getNanos() >= uploadNagDeadline) {
             new ItemToast(minecraft, displayStack, NO_RESPONSE_TITLE, NO_RESPONSE_MSG, ItemToast.TRANSFER_NO_RESPONSE_TOKEN)
@@ -104,7 +110,7 @@ public abstract class ComputerScreenBase<T extends ContainerComputerBase> extend
 
 
     @Override
-    public void render(@Nonnull PoseStack stack, int mouseX, int mouseY, float partialTicks) {
+    public void render(PoseStack stack, int mouseX, int mouseY, float partialTicks) {
         renderBackground(stack);
         super.render(stack, mouseX, mouseY, partialTicks);
         renderTooltip(stack, mouseX, mouseY);
@@ -127,12 +133,12 @@ public abstract class ComputerScreenBase<T extends ContainerComputerBase> extend
 
 
     @Override
-    protected void renderLabels(@Nonnull PoseStack transform, int mouseX, int mouseY) {
+    protected void renderLabels(PoseStack transform, int mouseX, int mouseY) {
         // Skip rendering labels.
     }
 
     @Override
-    public void onFilesDrop(@Nonnull List<Path> files) {
+    public void onFilesDrop(List<Path> files) {
         if (files.isEmpty()) return;
 
         if (!menu.isOn()) {
@@ -193,7 +199,7 @@ public abstract class ComputerScreenBase<T extends ContainerComputerBase> extend
                 }
             }
             case CONSUMED -> uploadNagDeadline = Long.MAX_VALUE;
-            case ERROR -> alert(UploadResult.FAILED_TITLE, message);
+            case ERROR -> alert(UploadResult.FAILED_TITLE, assertNonNull(message));
         }
     }
 

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

@@ -13,8 +13,6 @@ import dan200.computercraft.shared.computer.inventory.ContainerComputerBase;
 import net.minecraft.network.chat.Component;
 import net.minecraft.world.entity.player.Inventory;
 
-import javax.annotation.Nonnull;
-
 import static dan200.computercraft.client.render.ComputerBorderRenderer.BORDER;
 import static dan200.computercraft.client.render.RenderTypes.FULL_BRIGHT_LIGHTMAP;
 
@@ -32,8 +30,9 @@ public final class GuiComputer<T extends ContainerComputerBase> extends Computer
     }
 
     @Override
-    public void renderBg(@Nonnull PoseStack stack, float partialTicks, int mouseX, int mouseY) {
+    public void renderBg(PoseStack stack, float partialTicks, int mouseX, int mouseY) {
         // Draw a border around the terminal
+        var terminal = getTerminal();
         ComputerBorderRenderer.render(
             stack.last().pose(), ComputerBorderRenderer.getTexture(family), terminal.x, terminal.y, getBlitOffset(),
             FULL_BRIGHT_LIGHTMAP, terminal.getWidth(), terminal.getHeight()

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

@@ -13,7 +13,6 @@ import net.minecraft.network.chat.Component;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.entity.player.Inventory;
 
-import javax.annotation.Nonnull;
 
 public class GuiDiskDrive extends AbstractContainerScreen<ContainerDiskDrive> {
     private static final ResourceLocation BACKGROUND = new ResourceLocation("computercraft", "textures/gui/disk_drive.png");
@@ -23,14 +22,14 @@ public class GuiDiskDrive extends AbstractContainerScreen<ContainerDiskDrive> {
     }
 
     @Override
-    protected void renderBg(@Nonnull PoseStack transform, float partialTicks, int mouseX, int mouseY) {
+    protected void renderBg(PoseStack transform, float partialTicks, int mouseX, int mouseY) {
         RenderSystem.setShaderColor(1.0F, 1.0F, 1.0F, 1.0F);
         RenderSystem.setShaderTexture(0, BACKGROUND);
         blit(transform, leftPos, topPos, 0, 0, imageWidth, imageHeight);
     }
 
     @Override
-    public void render(@Nonnull PoseStack transform, int mouseX, int mouseY, float partialTicks) {
+    public void render(PoseStack transform, int mouseX, int mouseY, float partialTicks) {
         renderBackground(transform);
         super.render(transform, mouseX, mouseY, partialTicks);
         renderTooltip(transform, mouseX, mouseY);

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

@@ -13,7 +13,6 @@ import net.minecraft.network.chat.Component;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.entity.player.Inventory;
 
-import javax.annotation.Nonnull;
 
 public class GuiPrinter extends AbstractContainerScreen<ContainerPrinter> {
     private static final ResourceLocation BACKGROUND = new ResourceLocation("computercraft", "textures/gui/printer.png");
@@ -23,7 +22,7 @@ public class GuiPrinter extends AbstractContainerScreen<ContainerPrinter> {
     }
 
     @Override
-    protected void renderBg(@Nonnull PoseStack transform, float partialTicks, int mouseX, int mouseY) {
+    protected void renderBg(PoseStack transform, float partialTicks, int mouseX, int mouseY) {
         RenderSystem.setShaderColor(1.0F, 1.0F, 1.0F, 1.0F);
         RenderSystem.setShaderTexture(0, BACKGROUND);
         blit(transform, leftPos, topPos, 0, 0, imageWidth, imageHeight);
@@ -32,7 +31,7 @@ public class GuiPrinter extends AbstractContainerScreen<ContainerPrinter> {
     }
 
     @Override
-    public void render(@Nonnull PoseStack stack, int mouseX, int mouseY, float partialTicks) {
+    public void render(PoseStack stack, int mouseX, int mouseY, float partialTicks) {
         renderBackground(stack);
         super.render(stack, mouseX, mouseY, partialTicks);
         renderTooltip(stack, mouseX, mouseY);

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

@@ -17,8 +17,6 @@ import net.minecraft.network.chat.Component;
 import net.minecraft.world.entity.player.Inventory;
 import org.lwjgl.glfw.GLFW;
 
-import javax.annotation.Nonnull;
-
 import static dan200.computercraft.client.render.PrintoutRenderer.*;
 import static dan200.computercraft.client.render.RenderTypes.FULL_BRIGHT_LIGHTMAP;
 
@@ -83,7 +81,7 @@ public class GuiPrintout extends AbstractContainerScreen<ContainerHeldItem> {
     }
 
     @Override
-    protected void renderBg(@Nonnull PoseStack transform, float partialTicks, int mouseX, int mouseY) {
+    protected void renderBg(PoseStack transform, float partialTicks, int mouseX, int mouseY) {
         // Draw the printout
         RenderSystem.setShaderColor(1.0f, 1.0f, 1.0f, 1.0f);
         RenderSystem.enableDepthTest();
@@ -95,7 +93,7 @@ public class GuiPrintout extends AbstractContainerScreen<ContainerHeldItem> {
     }
 
     @Override
-    public void render(@Nonnull PoseStack stack, int mouseX, int mouseY, float partialTicks) {
+    public void render(PoseStack stack, int mouseX, int mouseY, float partialTicks) {
         // We must take the background further back in order to not overlap with our printed pages.
         setBlitOffset(getBlitOffset() - 1);
         renderBackground(stack);
@@ -105,7 +103,7 @@ public class GuiPrintout extends AbstractContainerScreen<ContainerHeldItem> {
     }
 
     @Override
-    protected void renderLabels(@Nonnull PoseStack transform, int mouseX, int mouseY) {
+    protected void renderLabels(PoseStack transform, int mouseX, int mouseY) {
         // Skip rendering labels.
     }
 }

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

@@ -17,8 +17,6 @@ import net.minecraft.network.chat.Component;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.entity.player.Inventory;
 
-import javax.annotation.Nonnull;
-
 import static dan200.computercraft.shared.turtle.inventory.ContainerTurtle.*;
 
 public class GuiTurtle extends ComputerScreenBase<ContainerTurtle> {
@@ -44,7 +42,7 @@ public class GuiTurtle extends ComputerScreenBase<ContainerTurtle> {
     }
 
     @Override
-    protected void renderBg(@Nonnull PoseStack transform, float partialTicks, int mouseX, int mouseY) {
+    protected void renderBg(PoseStack transform, float partialTicks, int mouseX, int mouseY) {
         var advanced = family == ComputerFamily.ADVANCED;
         RenderSystem.setShaderTexture(0, advanced ? BACKGROUND_ADVANCED : BACKGROUND_NORMAL);
         blit(transform, leftPos + ComputerSidebar.WIDTH, topPos, 0, 0, TEX_WIDTH, TEX_HEIGHT);

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

@@ -14,7 +14,6 @@ import net.minecraft.network.chat.Component;
 import net.minecraft.util.FormattedCharSequence;
 import net.minecraft.world.item.ItemStack;
 
-import javax.annotation.Nonnull;
 import java.util.List;
 
 /**
@@ -68,15 +67,13 @@ public class ItemToast implements Toast {
         return MARGIN * 2 + LINE_SPACING + message.size() * LINE_SPACING;
     }
 
-    @Nonnull
     @Override
     public Object getToken() {
         return token;
     }
 
-    @Nonnull
     @Override
-    public Visibility render(@Nonnull PoseStack transform, @Nonnull ToastComponent component, long time) {
+    public Visibility render(PoseStack transform, ToastComponent component, long time) {
         if (isNew) {
 
             firstDisplay = time;

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

@@ -16,12 +16,14 @@ import net.minecraft.network.chat.Component;
 import net.minecraft.world.entity.player.Inventory;
 import org.lwjgl.glfw.GLFW;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+import static dan200.computercraft.core.util.Nullability.assertNonNull;
 
 public class NoTermComputerScreen<T extends ContainerComputerBase> extends Screen implements MenuAccess<T> {
     private final T menu;
     private final Terminal terminalData;
-    private WidgetTerminal terminal;
+    private @Nullable WidgetTerminal terminal;
 
     public NoTermComputerScreen(T menu, Inventory player, Component title) {
         super(title);
@@ -29,7 +31,6 @@ public class NoTermComputerScreen<T extends ContainerComputerBase> extends Scree
         terminalData = menu.getTerminal();
     }
 
-    @Nonnull
     @Override
     public T getMenu() {
         return menu;
@@ -62,7 +63,7 @@ public class NoTermComputerScreen<T extends ContainerComputerBase> extends Scree
     @Override
     public final void tick() {
         super.tick();
-        terminal.update();
+        assertNonNull(terminal).update();
     }
 
     @Override
@@ -93,7 +94,7 @@ public class NoTermComputerScreen<T extends ContainerComputerBase> extends Scree
     }
 
     @Override
-    public void render(@Nonnull PoseStack transform, int mouseX, int mouseY, float partialTicks) {
+    public void render(PoseStack transform, int mouseX, int mouseY, float partialTicks) {
         super.render(transform, mouseX, mouseY, partialTicks);
 
         var font = minecraft.font;

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

@@ -15,9 +15,11 @@ import net.minecraft.client.gui.screens.Screen;
 import net.minecraft.network.chat.Component;
 import net.minecraft.resources.ResourceLocation;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.List;
 
+import static dan200.computercraft.core.util.Nullability.assertNonNull;
+
 public final class OptionScreen extends Screen {
     private static final ResourceLocation BACKGROUND = new ResourceLocation("computercraft", "textures/gui/blank_screen.png");
 
@@ -32,7 +34,7 @@ public final class OptionScreen extends Screen {
     private int innerWidth;
     private int innerHeight;
 
-    private MultiLineLabel messageRenderer;
+    private @Nullable MultiLineLabel messageRenderer;
     private final Component message;
     private final List<AbstractWidget> buttons;
     private final Runnable exit;
@@ -81,7 +83,7 @@ public final class OptionScreen extends Screen {
     }
 
     @Override
-    public void render(@Nonnull PoseStack transform, int mouseX, int mouseY, float partialTicks) {
+    public void render(PoseStack transform, int mouseX, int mouseY, float partialTicks) {
         renderBackground(transform);
 
         // Render the actual texture.
@@ -93,7 +95,7 @@ public final class OptionScreen extends Screen {
         );
         blit(transform, x, y + innerHeight - PADDING, 0, 256 - PADDING, innerWidth, PADDING);
 
-        messageRenderer.renderLeftAlignedNoShadow(transform, x + PADDING, y + PADDING, FONT_HEIGHT, 0x404040);
+        assertNonNull(messageRenderer).renderLeftAlignedNoShadow(transform, x + PADDING, y + PADDING, FONT_HEIGHT, 0x404040);
         super.render(transform, mouseX, mouseY, partialTicks);
     }
 
@@ -110,7 +112,6 @@ public final class OptionScreen extends Screen {
         for (var widget : buttons) widget.active = false;
     }
 
-    @Nonnull
     public Screen getOriginalScreen() {
         return originalScreen;
     }

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

@@ -12,7 +12,6 @@ import net.minecraft.client.gui.screens.Screen;
 import net.minecraft.network.chat.Component;
 import net.minecraft.resources.ResourceLocation;
 
-import javax.annotation.Nonnull;
 import java.util.List;
 import java.util.function.IntSupplier;
 import java.util.function.Supplier;
@@ -61,7 +60,7 @@ public class DynamicImageButton extends Button {
     }
 
     @Override
-    public void renderButton(@Nonnull PoseStack stack, int mouseX, int mouseY, float partialTicks) {
+    public void renderButton(PoseStack stack, int mouseX, int mouseY, float partialTicks) {
         RenderSystem.setShaderTexture(0, texture);
         RenderSystem.disableDepthTest();
 
@@ -74,7 +73,6 @@ public class DynamicImageButton extends Button {
         if (isHovered) renderToolTip(stack, mouseX, mouseY);
     }
 
-    @Nonnull
     @Override
     public Component getMessage() {
         var tooltip = this.tooltip.get();
@@ -82,7 +80,7 @@ public class DynamicImageButton extends Button {
     }
 
     @Override
-    public void renderToolTip(@Nonnull PoseStack stack, int mouseX, int mouseY) {
+    public void renderToolTip(PoseStack stack, int mouseX, int mouseY) {
         var tooltip = this.tooltip.get();
         if (!tooltip.isEmpty()) {
             screen.renderComponentTooltip(stack, tooltip, mouseX, mouseY);

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

@@ -19,7 +19,6 @@ import net.minecraft.client.renderer.MultiBufferSource;
 import net.minecraft.network.chat.Component;
 import org.lwjgl.glfw.GLFW;
 
-import javax.annotation.Nonnull;
 import java.util.BitSet;
 
 import static dan200.computercraft.client.render.ComputerBorderRenderer.MARGIN;
@@ -29,8 +28,8 @@ import static dan200.computercraft.client.render.text.FixedWidthFontRenderer.FON
 public class WidgetTerminal extends AbstractWidget {
     private static final float TERMINATE_TIME = 0.5f;
 
-    private final @Nonnull Terminal terminal;
+    private final Terminal terminal;
-    private final @Nonnull InputHandler computer;
+    private final InputHandler computer;
 
     // The positions of the actual terminal
     private final int innerX;
@@ -48,7 +47,7 @@ public class WidgetTerminal extends AbstractWidget {
 
     private final BitSet keysDown = new BitSet(256);
 
-    public WidgetTerminal(@Nonnull Terminal terminal, @Nonnull InputHandler computer, int x, int y) {
+    public WidgetTerminal(Terminal terminal, InputHandler computer, int x, int y) {
         super(x, y, terminal.getWidth() * FONT_WIDTH + MARGIN * 2, terminal.getHeight() * FONT_HEIGHT + MARGIN * 2, Component.empty());
 
         this.terminal = terminal;
@@ -264,7 +263,7 @@ public class WidgetTerminal extends AbstractWidget {
     }
 
     @Override
-    public void render(@Nonnull PoseStack transform, int mouseX, int mouseY, float partialTicks) {
+    public void render(PoseStack transform, int mouseX, int mouseY, float partialTicks) {
         if (!visible) return;
 
         var bufferSource = MultiBufferSource.immediate(Tesselator.getInstance().getBuilder());
@@ -279,7 +278,7 @@ public class WidgetTerminal extends AbstractWidget {
     }
 
     @Override
-    public void updateNarration(@Nonnull NarrationElementOutput output) {
+    public void updateNarration(NarrationElementOutput output) {
         // I'm not sure what the right option is here.
     }
 

src/main/java/dan200/computercraft/client/platform/AbstractClientNetworkContext.java

@@ -26,6 +26,7 @@ import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.entity.player.Player;
 import net.minecraft.world.level.Level;
 
+import javax.annotation.Nullable;
 import java.util.UUID;
 
 /**
@@ -96,7 +97,7 @@ public abstract class AbstractClientNetworkContext implements ClientNetworkConte
     }
 
     @Override
-    public final void handleUploadResult(int containerId, UploadResult result, Component errorMessage) {
+    public final void handleUploadResult(int containerId, UploadResult result, @Nullable Component errorMessage) {
         var minecraft = Minecraft.getInstance();
 
         var screen = OptionScreen.unwrap(minecraft.screen);

src/main/java/dan200/computercraft/client/pocket/ClientPocketComputers.java

@@ -14,8 +14,6 @@ import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
 import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
 import net.minecraft.world.item.ItemStack;
 
-import javax.annotation.Nonnull;
-
 /**
  * Maps {@link ServerComputer#getInstanceID()} to locals {@link PocketComputerData}.
  * <p>
@@ -42,14 +40,12 @@ public final class ClientPocketComputers {
      * @param advanced   Whether this computer has an advanced terminal.
      * @return The pocket computer data.
      */
-    @Nonnull
     public static PocketComputerData get(int instanceId, boolean advanced) {
         var computer = instances.get(instanceId);
         if (computer == null) instances.put(instanceId, computer = new PocketComputerData(advanced));
         return computer;
     }
 
-    @Nonnull
     public static PocketComputerData get(ItemStack stack) {
         var family = stack.getItem() instanceof ItemComputer computer ? computer.getFamily() : ComputerFamily.NORMAL;
         return get(ItemPocketComputer.getInstanceID(stack), family != ComputerFamily.NORMAL);

src/main/java/dan200/computercraft/client/pocket/PocketComputerData.java

@@ -12,8 +12,6 @@ import dan200.computercraft.shared.computer.terminal.NetworkedTerminal;
 import dan200.computercraft.shared.computer.terminal.TerminalState;
 import dan200.computercraft.shared.pocket.core.PocketServerComputer;
 
-import javax.annotation.Nonnull;
-
 /**
  * Clientside data about a pocket computer.
  * <p>
@@ -37,7 +35,6 @@ public class PocketComputerData {
         return state != ComputerState.OFF ? lightColour : -1;
     }
 
-    @Nonnull
     public Terminal getTerminal() {
         return terminal;
     }

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

@@ -14,8 +14,6 @@ import net.minecraft.client.renderer.MultiBufferSource;
 import net.minecraft.client.renderer.RenderType;
 import net.minecraft.resources.ResourceLocation;
 
-import javax.annotation.Nonnull;
-
 public class ComputerBorderRenderer {
     public static final ResourceLocation BACKGROUND_NORMAL = new ResourceLocation(ComputerCraft.MOD_ID, "textures/gui/corners_normal.png");
     public static final ResourceLocation BACKGROUND_ADVANCED = new ResourceLocation(ComputerCraft.MOD_ID, "textures/gui/corners_advanced.png");
@@ -61,8 +59,7 @@ public class ComputerBorderRenderer {
         this.b = b;
     }
 
-    @Nonnull
+    public static ResourceLocation getTexture(ComputerFamily family) {
-    public static ResourceLocation getTexture(@Nonnull ComputerFamily family) {
         return switch (family) {
             case NORMAL -> BACKGROUND_NORMAL;
             case ADVANCED -> BACKGROUND_ADVANCED;

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

@@ -36,7 +36,7 @@ public class MonitorTextureBufferShader extends ShaderInstance {
     private final int monitorData;
     private int uniformBuffer = 0;
 
-    private final Uniform cursorBlink;
+    private final @Nullable Uniform cursorBlink;
 
     public MonitorTextureBufferShader(ResourceProvider provider, ResourceLocation location, VertexFormat format) throws IOException {
         super(provider, location, format);

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

@@ -16,15 +16,16 @@ import net.minecraft.client.renderer.ShaderInstance;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.server.packs.resources.ResourceManager;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.io.IOException;
+import java.util.Objects;
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
 
 public class RenderTypes {
     public static final int FULL_BRIGHT_LIGHTMAP = (0xF << 4) | (0xF << 20);
 
-    private static MonitorTextureBufferShader monitorTboShader;
+    private static @Nullable MonitorTextureBufferShader monitorTboShader;
 
     /**
      * Renders a fullbright terminal.
@@ -49,15 +50,13 @@ public class RenderTypes {
      */
     public static final RenderType PRINTOUT_BACKGROUND = RenderType.text(new ResourceLocation("computercraft", "textures/gui/printout.png"));
 
-    @Nonnull
     static MonitorTextureBufferShader getMonitorTextureBufferShader() {
         if (monitorTboShader == null) throw new NullPointerException("MonitorTboShader has not been registered");
         return monitorTboShader;
     }
 
-    @Nonnull
     static ShaderInstance getTerminalShader() {
-        return GameRenderer.getRendertypeTextShader();
+        return Objects.requireNonNull(GameRenderer.getRendertypeTextShader(), "Text shader has not been registered");
     }
 
     public static void registerShaders(ResourceManager resources, BiConsumer<ShaderInstance, Consumer<ShaderInstance>> load) throws IOException {

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

@@ -21,6 +21,7 @@ import dan200.computercraft.client.render.text.DirectFixedWidthFontRenderer;
 import dan200.computercraft.client.render.text.FixedWidthFontRenderer;
 import dan200.computercraft.client.util.DirectBuffers;
 import dan200.computercraft.client.util.DirectVertexBuffer;
+import dan200.computercraft.core.terminal.Terminal;
 import dan200.computercraft.shared.integration.ShaderMod;
 import dan200.computercraft.shared.peripheral.monitor.ClientMonitor;
 import dan200.computercraft.shared.peripheral.monitor.MonitorRenderer;
@@ -34,12 +35,13 @@ import org.lwjgl.opengl.GL11;
 import org.lwjgl.opengl.GL20;
 import org.lwjgl.opengl.GL31;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.nio.ByteBuffer;
 import java.util.function.Consumer;
 
 import static dan200.computercraft.client.render.text.FixedWidthFontRenderer.FONT_HEIGHT;
 import static dan200.computercraft.client.render.text.FixedWidthFontRenderer.FONT_WIDTH;
+import static dan200.computercraft.core.util.Nullability.assertNonNull;
 
 public class TileEntityMonitorRenderer implements BlockEntityRenderer<TileMonitor> {
     /**
@@ -50,13 +52,13 @@ public class TileEntityMonitorRenderer implements BlockEntityRenderer<TileMonito
 
     private static final Matrix3f IDENTITY_NORMAL = Util.make(new Matrix3f(), Matrix3f::setIdentity);
 
-    private static ByteBuffer backingBuffer;
+    private static @Nullable ByteBuffer backingBuffer;
 
     public TileEntityMonitorRenderer(BlockEntityRendererProvider.Context context) {
     }
 
     @Override
-    public void render(@Nonnull TileMonitor monitor, float partialTicks, @Nonnull PoseStack transform, @Nonnull MultiBufferSource bufferSource, int lightmapCoord, int overlayLight) {
+    public void render(TileMonitor monitor, float partialTicks, PoseStack transform, MultiBufferSource bufferSource, int lightmapCoord, int overlayLight) {
         // Render from the origin monitor
         var originTerminal = monitor.getClientMonitor();
 
@@ -114,7 +116,7 @@ public class TileEntityMonitorRenderer implements BlockEntityRenderer<TileMonito
 
             var matrix = transform.last().pose();
 
-            renderTerminal(matrix, originTerminal, (float) (MARGIN / xScale), (float) (MARGIN / yScale));
+            renderTerminal(matrix, originTerminal, terminal, (float) (MARGIN / xScale), (float) (MARGIN / yScale));
 
             transform.popPose();
         } else {
@@ -128,8 +130,7 @@ public class TileEntityMonitorRenderer implements BlockEntityRenderer<TileMonito
         transform.popPose();
     }
 
-    private static void renderTerminal(Matrix4f matrix, ClientMonitor monitor, float xMargin, float yMargin) {
+    private static void renderTerminal(Matrix4f matrix, ClientMonitor monitor, Terminal terminal, float xMargin, float yMargin) {
-        var terminal = monitor.getTerminal();
         int width = terminal.getWidth(), height = terminal.getHeight();
         int pixelWidth = width * FONT_WIDTH, pixelHeight = height * FONT_HEIGHT;
 
@@ -167,8 +168,8 @@ public class TileEntityMonitorRenderer implements BlockEntityRenderer<TileMonito
                 RenderTypes.MONITOR_TBO.end(buffer, 0, 0, 0);
             }
             case VBO -> {
-                var backgroundBuffer = monitor.backgroundBuffer;
+                var backgroundBuffer = assertNonNull(monitor.backgroundBuffer);
-                var foregroundBuffer = monitor.foregroundBuffer;
+                var foregroundBuffer = assertNonNull(monitor.foregroundBuffer);
                 if (redraw) {
                     var size = DirectFixedWidthFontRenderer.getVertexCount(terminal);
 
@@ -236,7 +237,6 @@ public class TileEntityMonitorRenderer implements BlockEntityRenderer<TileMonito
         builder.vertex(matrix, x, y, 0).uv(x, y).endVertex();
     }
 
-    @Nonnull
     private static ByteBuffer getBuffer(int capacity) {
 
         var buffer = backingBuffer;

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

@@ -30,7 +30,7 @@ import net.minecraft.util.RandomSource;
 import net.minecraft.world.phys.BlockHitResult;
 import net.minecraft.world.phys.HitResult;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.List;
 
 public class TileEntityTurtleRenderer implements BlockEntityRenderer<TileTurtle> {
@@ -54,14 +54,14 @@ public class TileEntityTurtleRenderer implements BlockEntityRenderer<TileTurtle>
         };
     }
 
-    public static ResourceLocation getTurtleOverlayModel(ResourceLocation overlay, boolean christmas) {
+    public static @Nullable ResourceLocation getTurtleOverlayModel(@Nullable ResourceLocation overlay, boolean christmas) {
         if (overlay != null) return overlay;
         if (christmas) return ELF_OVERLAY_MODEL;
         return null;
     }
 
     @Override
-    public void render(@Nonnull TileTurtle turtle, float partialTicks, @Nonnull PoseStack transform, @Nonnull MultiBufferSource buffers, int lightmapCoord, int overlayLight) {
+    public void render(TileTurtle turtle, float partialTicks, PoseStack transform, MultiBufferSource buffers, int lightmapCoord, int overlayLight) {
         // Render the label
         var label = turtle.getLabel();
         var hit = renderer.cameraHitResult;
@@ -119,7 +119,7 @@ public class TileEntityTurtleRenderer implements BlockEntityRenderer<TileTurtle>
         transform.popPose();
     }
 
-    private void renderUpgrade(@Nonnull PoseStack transform, @Nonnull VertexConsumer renderer, int lightmapCoord, int overlayLight, TileTurtle turtle, TurtleSide side, float f) {
+    private void renderUpgrade(PoseStack transform, VertexConsumer renderer, int lightmapCoord, int overlayLight, TileTurtle turtle, TurtleSide side, float f) {
         var upgrade = turtle.getUpgrade(side);
         if (upgrade == null) return;
         transform.pushPose();
@@ -137,12 +137,12 @@ public class TileEntityTurtleRenderer implements BlockEntityRenderer<TileTurtle>
         transform.popPose();
     }
 
-    private void renderModel(@Nonnull PoseStack transform, @Nonnull VertexConsumer renderer, int lightmapCoord, int overlayLight, ResourceLocation modelLocation, int[] tints) {
+    private void renderModel(PoseStack transform, VertexConsumer renderer, int lightmapCoord, int overlayLight, ResourceLocation modelLocation, @Nullable int[] tints) {
         var modelManager = Minecraft.getInstance().getItemRenderer().getItemModelShaper().getModelManager();
         renderModel(transform, renderer, lightmapCoord, overlayLight, modelManager.getModel(modelLocation), tints);
     }
 
-    private void renderModel(@Nonnull PoseStack transform, @Nonnull VertexConsumer renderer, int lightmapCoord, int overlayLight, BakedModel model, int[] tints) {
+    private void renderModel(PoseStack transform, VertexConsumer renderer, int lightmapCoord, int overlayLight, BakedModel model, @Nullable int[] tints) {
         random.setSeed(0);
         renderQuads(transform, renderer, lightmapCoord, overlayLight, model.getQuads(null, null, random), tints);
         for (var facing : DirectionUtil.FACINGS) {
@@ -150,7 +150,7 @@ public class TileEntityTurtleRenderer implements BlockEntityRenderer<TileTurtle>
         }
     }
 
-    private static void renderQuads(@Nonnull PoseStack transform, @Nonnull VertexConsumer buffer, int lightmapCoord, int overlayLight, List<BakedQuad> quads, int[] tints) {
+    private static void renderQuads(PoseStack transform, VertexConsumer buffer, int lightmapCoord, int overlayLight, List<BakedQuad> quads, @Nullable int[] tints) {
         var matrix = transform.last();
 
         for (var bakedquad : quads) {

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

@@ -19,7 +19,6 @@ import net.minecraftforge.client.model.geometry.IGeometryBakingContext;
 import net.minecraftforge.client.model.geometry.IGeometryLoader;
 import net.minecraftforge.client.model.geometry.IUnbakedGeometry;
 
-import javax.annotation.Nonnull;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.Set;
@@ -33,9 +32,8 @@ public final class TurtleModelLoader implements IGeometryLoader<TurtleModelLoade
     private TurtleModelLoader() {
     }
 
-    @Nonnull
     @Override
-    public Unbaked read(@Nonnull JsonObject modelContents, @Nonnull JsonDeserializationContext deserializationContext) {
+    public Unbaked read(JsonObject modelContents, JsonDeserializationContext deserializationContext) {
         var model = new ResourceLocation(GsonHelper.getAsString(modelContents, "model"));
         return new Unbaked(model);
     }
@@ -57,10 +55,13 @@ public final class TurtleModelLoader implements IGeometryLoader<TurtleModelLoade
 
         @Override
         public BakedModel bake(IGeometryBakingContext owner, ModelBakery bakery, Function<Material, TextureAtlasSprite> spriteGetter, ModelState transform, ItemOverrides overrides, ResourceLocation modelLocation) {
-            return new TurtleModel(
+            var mainModel = bakery.bake(family, transform, spriteGetter);
-                bakery.bake(family, transform, spriteGetter),
+            if (mainModel == null) throw new NullPointerException(family + " failed to bake");
-                bakery.bake(COLOUR_TURTLE_MODEL, transform, spriteGetter)
+
-            );
+            var colourModel = bakery.bake(COLOUR_TURTLE_MODEL, transform, spriteGetter);
+            if (colourModel == null) throw new NullPointerException(COLOUR_TURTLE_MODEL + " failed to bake");
+
+            return new TurtleModel(mainModel, colourModel);
         }
     }
 }

src/main/java/dan200/computercraft/client/render/text/DirectFixedWidthFontRenderer.java

@@ -16,7 +16,6 @@ import dan200.computercraft.core.terminal.TextBuffer;
 import dan200.computercraft.core.util.Colour;
 import org.lwjgl.system.MemoryUtil;
 
-import javax.annotation.Nonnull;
 import java.nio.ByteBuffer;
 
 import static dan200.computercraft.client.render.text.FixedWidthFontRenderer.*;
@@ -65,7 +64,7 @@ public final class DirectFixedWidthFontRenderer {
     }
 
     private static void drawBackground(
-        @Nonnull QuadEmitter emitter, float x, float y, @Nonnull TextBuffer backgroundColour, @Nonnull Palette palette,
+        QuadEmitter emitter, float x, float y, TextBuffer backgroundColour, Palette palette,
         float leftMarginSize, float rightMarginSize, float height
     ) {
         if (leftMarginSize > 0) {
@@ -96,7 +95,7 @@ public final class DirectFixedWidthFontRenderer {
         }
     }
 
-    public static void drawString(@Nonnull QuadEmitter emitter, float x, float y, @Nonnull TextBuffer text, @Nonnull TextBuffer textColour, @Nonnull Palette palette) {
+    public static void drawString(QuadEmitter emitter, float x, float y, TextBuffer text, TextBuffer textColour, Palette palette) {
         for (var i = 0; i < text.length(); i++) {
             var colour = palette.getRenderColours(getColour(textColour.charAt(i), Colour.BLACK));
 
@@ -107,7 +106,7 @@ public final class DirectFixedWidthFontRenderer {
 
     }
 
-    public static void drawTerminalForeground(@Nonnull QuadEmitter emitter, float x, float y, @Nonnull Terminal terminal) {
+    public static void drawTerminalForeground(QuadEmitter emitter, float x, float y, Terminal terminal) {
         var palette = terminal.getPalette();
         var height = terminal.getHeight();
 
@@ -122,7 +121,7 @@ public final class DirectFixedWidthFontRenderer {
     }
 
     public static void drawTerminalBackground(
-        @Nonnull QuadEmitter emitter, float x, float y, @Nonnull Terminal terminal,
+        QuadEmitter emitter, float x, float y, Terminal terminal,
         float topMarginSize, float bottomMarginSize, float leftMarginSize, float rightMarginSize
     ) {
         var palette = terminal.getPalette();
@@ -149,7 +148,7 @@ public final class DirectFixedWidthFontRenderer {
         }
     }
 
-    public static void drawCursor(@Nonnull QuadEmitter emitter, float x, float y, @Nonnull Terminal terminal) {
+    public static void drawCursor(QuadEmitter emitter, float x, float y, Terminal terminal) {
         if (isCursorVisible(terminal)) {
             var colour = terminal.getPalette().getRenderColours(15 - terminal.getTextColour());
             drawChar(emitter, x + terminal.getCursorX() * FONT_WIDTH, y + terminal.getCursorY() * FONT_HEIGHT, '_', colour);

src/main/java/dan200/computercraft/client/render/text/FixedWidthFontRenderer.java

@@ -16,8 +16,6 @@ import dan200.computercraft.core.terminal.TextBuffer;
 import dan200.computercraft.core.util.Colour;
 import net.minecraft.resources.ResourceLocation;
 
-import javax.annotation.Nonnull;
-
 import static dan200.computercraft.client.render.RenderTypes.FULL_BRIGHT_LIGHTMAP;
 
 /**
@@ -88,7 +86,7 @@ public final class FixedWidthFontRenderer {
     }
 
     private static void drawBackground(
-        @Nonnull QuadEmitter emitter, float x, float y, @Nonnull TextBuffer backgroundColour, @Nonnull Palette palette,
+        QuadEmitter emitter, float x, float y, TextBuffer backgroundColour, Palette palette,
         float leftMarginSize, float rightMarginSize, float height, int light
     ) {
         if (leftMarginSize > 0) {
@@ -119,7 +117,7 @@ public final class FixedWidthFontRenderer {
         }
     }
 
-    public static void drawString(@Nonnull QuadEmitter emitter, float x, float y, @Nonnull TextBuffer text, @Nonnull TextBuffer textColour, @Nonnull Palette palette, int light) {
+    public static void drawString(QuadEmitter emitter, float x, float y, TextBuffer text, TextBuffer textColour, Palette palette, int light) {
         for (var i = 0; i < text.length(); i++) {
             var colour = palette.getRenderColours(getColour(textColour.charAt(i), Colour.BLACK));
 
@@ -130,7 +128,7 @@ public final class FixedWidthFontRenderer {
 
     }
 
-    public static void drawTerminalForeground(@Nonnull QuadEmitter emitter, float x, float y, @Nonnull Terminal terminal) {
+    public static void drawTerminalForeground(QuadEmitter emitter, float x, float y, Terminal terminal) {
         var palette = terminal.getPalette();
         var height = terminal.getHeight();
 
@@ -145,7 +143,7 @@ public final class FixedWidthFontRenderer {
     }
 
     public static void drawTerminalBackground(
-        @Nonnull QuadEmitter emitter, float x, float y, @Nonnull Terminal terminal,
+        QuadEmitter emitter, float x, float y, Terminal terminal,
         float topMarginSize, float bottomMarginSize, float leftMarginSize, float rightMarginSize
     ) {
         var palette = terminal.getPalette();
@@ -180,7 +178,7 @@ public final class FixedWidthFontRenderer {
         return cursorX >= 0 && cursorX < terminal.getWidth() && cursorY >= 0 && cursorY < terminal.getHeight();
     }
 
-    public static void drawCursor(@Nonnull QuadEmitter emitter, float x, float y, @Nonnull Terminal terminal) {
+    public static void drawCursor(QuadEmitter emitter, float x, float y, Terminal terminal) {
         if (isCursorVisible(terminal) && FrameInfo.getGlobalCursorBlink()) {
             var colour = terminal.getPalette().getRenderColours(15 - terminal.getTextColour());
             drawChar(emitter, x + terminal.getCursorX() * FONT_WIDTH, y + terminal.getCursorY() * FONT_HEIGHT, '_', colour, FULL_BRIGHT_LIGHTMAP);
@@ -188,7 +186,7 @@ public final class FixedWidthFontRenderer {
     }
 
     public static void drawTerminal(
-        @Nonnull QuadEmitter emitter, float x, float y, @Nonnull Terminal terminal,
+        QuadEmitter emitter, float x, float y, Terminal terminal,
         float topMarginSize, float bottomMarginSize, float leftMarginSize, float rightMarginSize
     ) {
         drawTerminalBackground(
@@ -208,7 +206,7 @@ public final class FixedWidthFontRenderer {
         emitter.poseMatrix().load(transformBackup);
     }
 
-    public static void drawEmptyTerminal(@Nonnull QuadEmitter emitter, float x, float y, float width, float height) {
+    public static void drawEmptyTerminal(QuadEmitter emitter, float x, float y, float width, float height) {
         drawQuad(emitter, x, y, 0, width, height, BLACK, FULL_BRIGHT_LIGHTMAP);
     }
 

src/main/java/dan200/computercraft/client/sound/DfpwmStream.java

@@ -12,7 +12,6 @@ import net.minecraft.client.sounds.AudioStream;
 import net.minecraft.client.sounds.SoundEngine;
 import org.lwjgl.BufferUtils;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import javax.sound.sampled.AudioFormat;
 import java.io.IOException;
@@ -55,7 +54,7 @@ class DfpwmStream implements AudioStream {
     DfpwmStream() {
     }
 
-    void push(@Nonnull ByteBuf input) {
+    void push(ByteBuf input) {
         var readable = input.readableBytes();
         var output = ByteBuffer.allocate(readable * 8).order(ByteOrder.nativeOrder());
 
@@ -101,13 +100,12 @@ class DfpwmStream implements AudioStream {
         }
     }
 
-    @Nonnull
     @Override
     public AudioFormat getFormat() {
         return MONO_8;
     }
 
-    @Nonnull
+    @Nullable
     @Override
     public synchronized ByteBuffer read(int capacity) {
         var result = BufferUtils.createByteBuffer(capacity);

src/main/java/dan200/computercraft/client/sound/SpeakerInstance.java

@@ -12,14 +12,16 @@ import io.netty.buffer.ByteBuf;
 import net.minecraft.client.Minecraft;
 import net.minecraft.resources.ResourceLocation;
 
+import javax.annotation.Nullable;
+
 /**
  * An instance of a speaker, which is either playing a {@link DfpwmStream} stream or a normal sound.
  */
 public class SpeakerInstance {
     public static final ResourceLocation DFPWM_STREAM = new ResourceLocation(ComputerCraft.MOD_ID, "speaker.dfpwm_fake_audio_should_not_be_played");
 
-    private DfpwmStream currentStream;
+    private @Nullable DfpwmStream currentStream;
-    private SpeakerSound sound;
+    private @Nullable SpeakerSound sound;
 
     SpeakerInstance() {
     }
@@ -30,7 +32,7 @@ public class SpeakerInstance {
         var stream = currentStream;
         if (stream == null) stream = currentStream = new DfpwmStream();
         var exhausted = stream.isEmpty();
-        currentStream.push(buffer);
+        stream.push(buffer);
 
         // If we've got nothing left in the buffer, enqueue an additional one just in case.
         if (exhausted && sound != null && sound.stream == stream && stream.channel != null && stream.executor != null) {

src/main/java/dan200/computercraft/client/sound/SpeakerSound.java

@@ -16,17 +16,18 @@ import net.minecraft.resources.ResourceLocation;
 import net.minecraft.sounds.SoundSource;
 import net.minecraft.world.entity.Entity;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.concurrent.CompletableFuture;
 
 public class SpeakerSound extends AbstractSoundInstance implements TickableSoundInstance {
+    @Nullable
     DfpwmStream stream;
 
-    private Entity entity;
+    private @Nullable Entity entity;
 
     private boolean stopped = false;
 
-    SpeakerSound(ResourceLocation sound, DfpwmStream stream, SpeakerPosition position, float volume, float pitch) {
+    SpeakerSound(ResourceLocation sound, @Nullable DfpwmStream stream, SpeakerPosition position, float volume, float pitch) {
         super(sound, SoundSource.RECORDS, SoundInstance.createUnseededRandom());
         setPosition(position);
         this.stream = stream;
@@ -60,13 +61,12 @@ public class SpeakerSound extends AbstractSoundInstance implements TickableSound
         }
     }
 
-    @Nonnull
     @Override
-    public CompletableFuture<AudioStream> getStream(@Nonnull SoundBufferLibrary soundBuffers, @Nonnull Sound sound, boolean looping) {
+    public CompletableFuture<AudioStream> getStream(SoundBufferLibrary soundBuffers, Sound sound, boolean looping) {
         return stream != null ? CompletableFuture.completedFuture(stream) : super.getStream(soundBuffers, sound, looping);
     }
 
-    public AudioStream getStream() {
+    public @Nullable AudioStream getStream() {
         return stream;
     }
 }

src/main/java/dan200/computercraft/client/turtle/TurtleModemModeller.java

@@ -14,8 +14,6 @@ import dan200.computercraft.shared.turtle.upgrades.TurtleModem;
 import net.minecraft.resources.ResourceLocation;
 import org.jetbrains.annotations.Nullable;
 
-import javax.annotation.Nonnull;
-
 public class TurtleModemModeller implements TurtleUpgradeModeller<TurtleModem> {
     private final ResourceLocation leftOffModel;
     private final ResourceLocation rightOffModel;
@@ -36,9 +34,8 @@ public class TurtleModemModeller implements TurtleUpgradeModeller<TurtleModem> {
         }
     }
 
-    @Nonnull
     @Override
-    public TransformedModel getModel(@Nonnull TurtleModem upgrade, @Nullable ITurtleAccess turtle, @Nonnull TurtleSide side) {
+    public TransformedModel getModel(TurtleModem upgrade, @Nullable ITurtleAccess turtle, TurtleSide side) {
         var active = false;
         if (turtle != null) {
             var turtleNBT = turtle.getUpgradeNBTData(side);

src/main/java/dan200/computercraft/client/turtle/TurtleUpgradeModellers.java

@@ -16,7 +16,6 @@ import dan200.computercraft.shared.TurtleUpgrades;
 import dan200.computercraft.shared.UpgradeManager;
 import net.minecraft.client.Minecraft;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.Map;
 import java.util.WeakHashMap;
@@ -39,7 +38,7 @@ public final class TurtleUpgradeModellers {
     private TurtleUpgradeModellers() {
     }
 
-    public static <T extends ITurtleUpgrade> void register(@Nonnull TurtleUpgradeSerialiser<T> serialiser, @Nonnull TurtleUpgradeModeller<T> modeller) {
+    public static <T extends ITurtleUpgrade> void register(TurtleUpgradeSerialiser<T> serialiser, TurtleUpgradeModeller<T> modeller) {
         synchronized (turtleModels) {
             if (turtleModels.containsKey(serialiser)) {
                 throw new IllegalStateException("Modeller already registered for serialiser");
@@ -49,7 +48,7 @@ public final class TurtleUpgradeModellers {
         }
     }
 
-    public static TransformedModel getModel(@Nonnull ITurtleUpgrade upgrade, @Nullable ITurtleAccess access, @Nonnull TurtleSide side) {
+    public static TransformedModel getModel(ITurtleUpgrade upgrade, @Nullable ITurtleAccess access, TurtleSide side) {
         @SuppressWarnings("unchecked")
         var modeller = (TurtleUpgradeModeller<ITurtleUpgrade>) modelCache.computeIfAbsent(upgrade, TurtleUpgradeModellers::getModeller);
         return modeller.getModel(upgrade, access, side);

src/main/java/dan200/computercraft/data/LootTableGenerator.java

@@ -35,7 +35,6 @@ import net.minecraft.world.level.storage.loot.predicates.LootItemBlockStatePrope
 import net.minecraft.world.level.storage.loot.predicates.LootItemCondition;
 import net.minecraft.world.level.storage.loot.providers.number.ConstantValue;
 
-import javax.annotation.Nonnull;
 import java.util.List;
 import java.util.Map;
 import java.util.function.BiConsumer;
@@ -47,7 +46,6 @@ class LootTableGenerator extends LootTableProvider {
         super(generator);
     }
 
-    @Nonnull
     @Override
     public List<Pair<Supplier<Consumer<BiConsumer<ResourceLocation, LootTable.Builder>>>, LootContextParamSet>> getTables() {
         return List.of(
@@ -57,7 +55,7 @@ class LootTableGenerator extends LootTableProvider {
     }
 
     @Override
-    protected void validate(Map<ResourceLocation, LootTable> map, @Nonnull ValidationContext validationtracker) {
+    protected void validate(Map<ResourceLocation, LootTable> map, ValidationContext validationtracker) {
         map.forEach((id, table) -> LootTables.validate(validationtracker, id, table));
     }
 

src/main/java/dan200/computercraft/data/ModelProvider.java

@@ -22,7 +22,6 @@ import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.item.Item;
 import net.minecraft.world.level.block.Block;
 
-import javax.annotation.Nonnull;
 import java.nio.file.Path;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -56,7 +55,7 @@ public class ModelProvider implements DataProvider {
     }
 
     @Override
-    public void run(@Nonnull CachedOutput output) {
+    public void run(CachedOutput output) {
         Map<Block, BlockStateGenerator> blockStates = new HashMap<>();
         Consumer<BlockStateGenerator> addBlockState = generator -> {
             var block = generator.getBlock();
@@ -102,7 +101,6 @@ public class ModelProvider implements DataProvider {
         }
     }
 
-    @Nonnull
     @Override
     public String getName() {
         return "Block State Definitions";

src/main/java/dan200/computercraft/data/PocketUpgradeGenerator.java

@@ -11,7 +11,6 @@ import dan200.computercraft.api.pocket.PocketUpgradeSerialiser;
 import net.minecraft.data.DataGenerator;
 import net.minecraft.resources.ResourceLocation;
 
-import javax.annotation.Nonnull;
 import java.util.function.Consumer;
 
 import static dan200.computercraft.shared.ModRegistry.Items;
@@ -23,14 +22,13 @@ class PocketUpgradeGenerator extends PocketUpgradeDataProvider {
     }
 
     @Override
-    protected void addUpgrades(@Nonnull Consumer<Upgrade<PocketUpgradeSerialiser<?>>> addUpgrade) {
+    protected void addUpgrades(Consumer<Upgrade<PocketUpgradeSerialiser<?>>> addUpgrade) {
         addUpgrade.accept(simpleWithCustomItem(id("speaker"), PocketUpgradeSerialisers.SPEAKER.get(), Items.SPEAKER.get()));
         simpleWithCustomItem(id("wireless_modem_normal"), PocketUpgradeSerialisers.WIRELESS_MODEM_NORMAL.get(), Items.WIRELESS_MODEM_NORMAL.get()).add(addUpgrade);
         simpleWithCustomItem(id("wireless_modem_advanced"), PocketUpgradeSerialisers.WIRELESS_MODEM_ADVANCED.get(), Items.WIRELESS_MODEM_ADVANCED.get()).add(addUpgrade);
     }
 
-    @Nonnull
+    private static ResourceLocation id(String id) {
-    private static ResourceLocation id(@Nonnull String id) {
         return new ResourceLocation(ComputerCraft.MOD_ID, id);
     }
 }

src/main/java/dan200/computercraft/data/PrettyJsonWriter.java

@@ -5,7 +5,6 @@
  */
 package dan200.computercraft.data;
 
-import com.google.common.base.Strings;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonElement;
@@ -243,7 +242,7 @@ public class PrettyJsonWriter extends JsonWriter {
                 }
             } else {
                 // We've run out of room, so write each value on separate lines.
-                var indentStr = Strings.repeat(" ", indent);
+                var indentStr = " ".repeat(indent);
                 writer.append("\n  ").append(indentStr);
 
                 var comma = false;

src/main/java/dan200/computercraft/data/RecipeGenerator.java

@@ -38,7 +38,6 @@ import net.minecraft.world.item.crafting.SimpleRecipeSerializer;
 import net.minecraft.world.level.ItemLike;
 import net.minecraft.world.level.block.Blocks;
 
-import javax.annotation.Nonnull;
 import java.util.Locale;
 import java.util.function.Consumer;
 
@@ -58,7 +57,7 @@ class RecipeGenerator extends RecipeProvider {
     }
 
     @Override
-    protected void buildCraftingRecipes(@Nonnull Consumer<FinishedRecipe> add) {
+    protected void buildCraftingRecipes(Consumer<FinishedRecipe> add) {
         basicRecipes(add);
         diskColours(add);
         pocketUpgrades(add);
@@ -76,7 +75,7 @@ class RecipeGenerator extends RecipeProvider {
      *
      * @param add The callback to add recipes.
      */
-    private void diskColours(@Nonnull Consumer<FinishedRecipe> add) {
+    private void diskColours(Consumer<FinishedRecipe> add) {
         for (var colour : Colour.VALUES) {
             ShapelessRecipeBuilder
                 .shapeless(ModRegistry.Items.DISK.get())
@@ -98,7 +97,7 @@ class RecipeGenerator extends RecipeProvider {
      *
      * @param add The callback to add recipes.
      */
-    private void turtleUpgrades(@Nonnull Consumer<FinishedRecipe> add) {
+    private void turtleUpgrades(Consumer<FinishedRecipe> add) {
         for (var family : ComputerFamily.values()) {
             var base = TurtleItemFactory.create(-1, null, -1, family, null, null, 0, null);
             if (base.isEmpty()) continue;
@@ -130,7 +129,7 @@ class RecipeGenerator extends RecipeProvider {
      *
      * @param add The callback to add recipes.
      */
-    private void pocketUpgrades(@Nonnull Consumer<FinishedRecipe> add) {
+    private void pocketUpgrades(Consumer<FinishedRecipe> add) {
         for (var family : ComputerFamily.values()) {
             var base = PocketComputerItemFactory.create(-1, null, -1, family, null);
             if (base.isEmpty()) continue;
@@ -158,7 +157,7 @@ class RecipeGenerator extends RecipeProvider {
         }
     }
 
-    private void basicRecipes(@Nonnull Consumer<FinishedRecipe> add) {
+    private void basicRecipes(Consumer<FinishedRecipe> add) {
         ShapedRecipeBuilder
             .shaped(ModRegistry.Items.CABLE.get(), 6)
             .pattern(" # ")

src/main/java/dan200/computercraft/data/RecipeWrapper.java

@@ -12,7 +12,6 @@ import net.minecraft.resources.ResourceLocation;
 import net.minecraft.util.GsonHelper;
 import net.minecraft.world.item.crafting.RecipeSerializer;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.ArrayList;
 import java.util.List;
@@ -65,18 +64,16 @@ final class RecipeWrapper implements Consumer<FinishedRecipe> {
         FinishedRecipe recipe, RecipeSerializer<?> serializer, List<Consumer<JsonObject>> extend
     ) implements FinishedRecipe {
         @Override
-        public void serializeRecipeData(@Nonnull JsonObject jsonObject) {
+        public void serializeRecipeData(JsonObject jsonObject) {
             recipe.serializeRecipeData(jsonObject);
             for (var extender : extend) extender.accept(jsonObject);
         }
 
-        @Nonnull
         @Override
         public ResourceLocation getId() {
             return recipe.getId();
         }
 
-        @Nonnull
         @Override
         public RecipeSerializer<?> getType() {
             return serializer;

src/main/java/dan200/computercraft/data/TurtleUpgradeGenerator.java

@@ -12,7 +12,6 @@ import dan200.computercraft.api.turtle.TurtleUpgradeSerialiser;
 import net.minecraft.data.DataGenerator;
 import net.minecraft.resources.ResourceLocation;
 
-import javax.annotation.Nonnull;
 import java.util.function.Consumer;
 
 import static dan200.computercraft.shared.ModRegistry.Items;
@@ -24,7 +23,7 @@ class TurtleUpgradeGenerator extends TurtleUpgradeDataProvider {
     }
 
     @Override
-    protected void addUpgrades(@Nonnull Consumer<Upgrade<TurtleUpgradeSerialiser<?>>> addUpgrade) {
+    protected void addUpgrades(Consumer<Upgrade<TurtleUpgradeSerialiser<?>>> addUpgrade) {
         simpleWithCustomItem(id("speaker"), TurtleSerialisers.SPEAKER.get(), Items.SPEAKER.get()).add(addUpgrade);
         simpleWithCustomItem(vanilla("crafting_table"), TurtleSerialisers.WORKBENCH.get(), net.minecraft.world.item.Items.CRAFTING_TABLE).add(addUpgrade);
         simpleWithCustomItem(id("wireless_modem_normal"), TurtleSerialisers.WIRELESS_MODEM_NORMAL.get(), Items.WIRELESS_MODEM_NORMAL.get()).add(addUpgrade);
@@ -37,13 +36,11 @@ class TurtleUpgradeGenerator extends TurtleUpgradeDataProvider {
         tool(vanilla("diamond_sword"), net.minecraft.world.item.Items.DIAMOND_SWORD).breakable(Blocks.TURTLE_SWORD_BREAKABLE).damageMultiplier(9.0f).add(addUpgrade);
     }
 
-    @Nonnull
+    private static ResourceLocation id(String id) {
-    private static ResourceLocation id(@Nonnull String id) {
         return new ResourceLocation(ComputerCraft.MOD_ID, id);
     }
 
-    @Nonnull
+    private static ResourceLocation vanilla(String id) {
-    private static ResourceLocation vanilla(@Nonnull String id) {
         // Naughty, please don't do this. Mostly here for some semblance of backwards compatibility.
         return new ResourceLocation("minecraft", id);
     }

src/main/java/dan200/computercraft/package-info.java

@@ -0,0 +1,22 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2022. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+/**
+ * ComputerCraft's core Lua runtime and APIs.
+ * <p>
+ * This is not considered part of the stable API, and so should not be consumed by other Minecraft mods. However,
+ * emulators or other CC-tooling may find this useful.
+ */
+@DefaultQualifier(value = NonNull.class, locations = {
+    TypeUseLocation.RETURN,
+    TypeUseLocation.PARAMETER,
+    TypeUseLocation.FIELD,
+})
+package dan200.computercraft;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+import org.checkerframework.framework.qual.TypeUseLocation;

src/main/java/dan200/computercraft/shared/BundledRedstone.java

@@ -12,7 +12,6 @@ import net.minecraft.core.BlockPos;
 import net.minecraft.core.Direction;
 import net.minecraft.world.level.Level;
 
-import javax.annotation.Nonnull;
 import java.util.ArrayList;
 import java.util.Objects;
 
@@ -22,12 +21,12 @@ public final class BundledRedstone {
     private BundledRedstone() {
     }
 
-    public static synchronized void register(@Nonnull IBundledRedstoneProvider provider) {
+    public static synchronized void register(IBundledRedstoneProvider provider) {
         Objects.requireNonNull(provider, "provider cannot be null");
         if (!providers.contains(provider)) providers.add(provider);
     }
 
-    public static int getDefaultOutput(@Nonnull Level world, @Nonnull BlockPos pos, @Nonnull Direction side) {
+    public static int getDefaultOutput(Level world, BlockPos pos, Direction side) {
         return world.isInWorldBounds(pos) ? DefaultBundledRedstoneProvider.getDefaultBundledRedstoneOutput(world, pos, side) : -1;
     }
 

src/main/java/dan200/computercraft/shared/MediaProviders.java

@@ -10,7 +10,7 @@ import dan200.computercraft.api.media.IMedia;
 import dan200.computercraft.api.media.IMediaProvider;
 import net.minecraft.world.item.ItemStack;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.LinkedHashSet;
 import java.util.Objects;
 import java.util.Set;
@@ -21,12 +21,12 @@ public final class MediaProviders {
     private MediaProviders() {
     }
 
-    public static synchronized void register(@Nonnull IMediaProvider provider) {
+    public static synchronized void register(IMediaProvider provider) {
         Objects.requireNonNull(provider, "provider cannot be null");
         providers.add(provider);
     }
 
-    public static IMedia get(@Nonnull ItemStack stack) {
+    public static @Nullable IMedia get(ItemStack stack) {
         if (stack.isEmpty()) return null;
 
         // Try the handlers in order:

src/main/java/dan200/computercraft/shared/Peripherals.java

@@ -15,7 +15,6 @@ import net.minecraft.core.Direction;
 import net.minecraft.world.level.Level;
 import net.minecraftforge.common.util.NonNullConsumer;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.Collection;
 import java.util.LinkedHashSet;
@@ -29,7 +28,7 @@ public final class Peripherals {
     private Peripherals() {
     }
 
-    public static synchronized void register(@Nonnull IPeripheralProvider provider) {
+    public static synchronized void register(IPeripheralProvider provider) {
         Objects.requireNonNull(provider, "provider cannot be null");
         providers.add(provider);
     }

src/main/java/dan200/computercraft/shared/UpgradeManager.java

@@ -21,7 +21,6 @@ import net.minecraft.world.item.ItemStack;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.Collection;
 import java.util.Collections;
@@ -42,7 +41,7 @@ public class UpgradeManager<R extends UpgradeSerialiser<? extends T>, T extends
     private static final Gson GSON = new GsonBuilder().setPrettyPrinting().disableHtmlEscaping().create();
 
     public record UpgradeWrapper<R extends UpgradeSerialiser<? extends T>, T extends IUpgradeBase>(
-        @Nonnull String id, @Nonnull T upgrade, @Nonnull R serialiser, @Nonnull String modId
+        String id, T upgrade, R serialiser, String modId
     ) {
     }
 
@@ -52,7 +51,7 @@ public class UpgradeManager<R extends UpgradeSerialiser<? extends T>, T extends
     private Map<String, UpgradeWrapper<R, T>> current = Collections.emptyMap();
     private Map<T, UpgradeWrapper<R, T>> currentWrappers = Collections.emptyMap();
 
-    public UpgradeManager(@Nonnull String kind, @Nonnull String path, @Nonnull ResourceKey<Registry<R>> registry) {
+    public UpgradeManager(String kind, String path, ResourceKey<Registry<R>> registry) {
         super(GSON, path);
         this.kind = kind;
         this.registry = registry;
@@ -65,18 +64,18 @@ public class UpgradeManager<R extends UpgradeSerialiser<? extends T>, T extends
     }
 
     @Nullable
-    public UpgradeWrapper<R, T> getWrapper(@Nonnull T upgrade) {
+    public UpgradeWrapper<R, T> getWrapper(T upgrade) {
         return currentWrappers.get(upgrade);
     }
 
     @Nullable
-    public String getOwner(@Nonnull T upgrade) {
+    public String getOwner(T upgrade) {
         var wrapper = currentWrappers.get(upgrade);
         return wrapper != null ? wrapper.modId() : null;
     }
 
     @Nullable
-    public T get(@Nonnull ItemStack stack) {
+    public T get(ItemStack stack) {
         if (stack.isEmpty()) return null;
 
         for (var wrapper : current.values()) {
@@ -89,18 +88,16 @@ public class UpgradeManager<R extends UpgradeSerialiser<? extends T>, T extends
         return null;
     }
 
-    @Nonnull
     public Collection<T> getUpgrades() {
         return currentWrappers.keySet();
     }
 
-    @Nonnull
     public Map<String, UpgradeWrapper<R, T>> getUpgradeWrappers() {
         return current;
     }
 
     @Override
-    protected void apply(@Nonnull Map<ResourceLocation, JsonElement> upgrades, @Nonnull ResourceManager manager, @Nonnull ProfilerFiller profiler) {
+    protected void apply(Map<ResourceLocation, JsonElement> upgrades, ResourceManager manager, ProfilerFiller profiler) {
         Map<String, UpgradeWrapper<R, T>> newUpgrades = new HashMap<>();
         for (var element : upgrades.entrySet()) {
             try {
@@ -136,7 +133,7 @@ public class UpgradeManager<R extends UpgradeSerialiser<? extends T>, T extends
         current.put(result.id(), result);
     }
 
-    public void loadFromNetwork(@Nonnull Map<String, UpgradeWrapper<R, T>> newUpgrades) {
+    public void loadFromNetwork(Map<String, UpgradeWrapper<R, T>> newUpgrades) {
         current = Collections.unmodifiableMap(newUpgrades);
         currentWrappers = newUpgrades.values().stream().collect(Collectors.toUnmodifiableMap(UpgradeWrapper::upgrade, x -> x));
     }

src/main/java/dan200/computercraft/shared/command/CommandComputerCraft.java

@@ -24,7 +24,6 @@ import net.minecraft.commands.CommandSourceStack;
 import net.minecraft.core.BlockPos;
 import net.minecraft.network.chat.Component;
 import net.minecraft.network.protocol.game.ClientboundPlayerPositionPacket;
-import net.minecraft.server.level.ServerLevel;
 import net.minecraft.server.level.ServerPlayer;
 import net.minecraft.world.MenuProvider;
 import net.minecraft.world.entity.player.Inventory;
@@ -33,7 +32,7 @@ import net.minecraft.world.inventory.AbstractContainerMenu;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.level.Level;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.io.File;
 import java.util.*;
 
@@ -150,11 +149,9 @@ public final class CommandComputerCraft {
                 .arg("computer", oneComputer())
                 .executes(context -> {
                     var computer = getComputerArgument(context, "computer");
-                    Level world = computer.getLevel();
+                    var world = computer.getLevel();
                     var pos = computer.getPosition();
 
-                    if (world == null || pos == null) throw TP_NOT_THERE.create();
-
                     var entity = context.getSource().getEntityOrException();
                     if (!(entity instanceof ServerPlayer player)) throw TP_NOT_PLAYER.create();
 
@@ -164,7 +161,7 @@ public final class CommandComputerCraft {
                             EnumSet.noneOf(ClientboundPlayerPositionPacket.RelativeArgument.class)
                         );
                     } else {
-                        player.teleportTo((ServerLevel) world,
+                        player.teleportTo(world,
                             pos.getX() + 0.5, pos.getY(), pos.getZ() + 0.5, 0, 0
                         );
                     }
@@ -198,15 +195,13 @@ public final class CommandComputerCraft {
                     var player = context.getSource().getPlayerOrException();
                     var computer = getComputerArgument(context, "computer");
                     new ComputerContainerData(computer, ItemStack.EMPTY).open(player, new MenuProvider() {
-                        @Nonnull
                         @Override
                         public Component getDisplayName() {
                             return Component.translatable("gui.computercraft.view_computer");
                         }
 
-                        @Nonnull
                         @Override
-                        public AbstractContainerMenu createMenu(int id, @Nonnull Inventory player, @Nonnull Player entity) {
+                        public AbstractContainerMenu createMenu(int id, Inventory player, Player entity) {
                             return new ContainerViewComputer(id, player, computer);
                         }
                     });
@@ -251,7 +246,7 @@ public final class CommandComputerCraft {
         );
     }
 
-    private static Component linkComputer(CommandSourceStack source, ServerComputer serverComputer, int computerId) {
+    private static Component linkComputer(CommandSourceStack source, @Nullable ServerComputer serverComputer, int computerId) {
         var out = Component.literal("");
 
         // Append the computer instance
@@ -305,7 +300,7 @@ public final class CommandComputerCraft {
         }
     }
 
-    private static Component linkStorage(CommandSourceStack source, int id) {
+    private static @Nullable Component linkStorage(CommandSourceStack source, int id) {
         var file = new File(ServerContext.get(source.getServer()).storageDir().toFile(), "computer/" + id);
         if (!file.isDirectory()) return null;
 
@@ -316,7 +311,6 @@ public final class CommandComputerCraft {
         );
     }
 
-    @Nonnull
     private static BasicComputerMetricsObserver getMetricsInstance(CommandSourceStack source) {
         var entity = source.getEntity();
         return ServerContext.get(source.getServer()).metrics().getMetricsInstance(entity instanceof Player ? entity.getUUID() : SYSTEM_UUID);

src/main/java/dan200/computercraft/shared/command/arguments/ComputersArgumentType.java

@@ -21,7 +21,6 @@ import net.minecraft.commands.synchronization.ArgumentTypeInfo;
 import net.minecraft.network.FriendlyByteBuf;
 import org.jetbrains.annotations.NotNull;
 
-import javax.annotation.Nonnull;
 import java.util.*;
 import java.util.concurrent.CompletableFuture;
 import java.util.function.Function;
@@ -145,19 +144,18 @@ public final class ComputersArgumentType implements ArgumentType<ComputersArgume
 
     public static class Info implements ArgumentTypeInfo<ComputersArgumentType, Template> {
         @Override
-        public void serializeToNetwork(@Nonnull ComputersArgumentType.Template arg, @Nonnull FriendlyByteBuf buf) {
+        public void serializeToNetwork(ComputersArgumentType.Template arg, FriendlyByteBuf buf) {
             buf.writeBoolean(arg.requireSome());
         }
 
-        @Nonnull
         @Override
-        public ComputersArgumentType.Template deserializeFromNetwork(@Nonnull FriendlyByteBuf buf) {
+        public ComputersArgumentType.Template deserializeFromNetwork(FriendlyByteBuf buf) {
             var requiresSome = buf.readBoolean();
             return new ComputersArgumentType.Template(this, requiresSome);
         }
 
         @Override
-        public void serializeToJson(@Nonnull ComputersArgumentType.Template arg, @Nonnull JsonObject json) {
+        public void serializeToJson(ComputersArgumentType.Template arg, JsonObject json) {
             json.addProperty("requireSome", arg.requireSome);
         }
 

src/main/java/dan200/computercraft/shared/command/arguments/RepeatArgumentType.java

@@ -20,7 +20,6 @@ import net.minecraft.network.FriendlyByteBuf;
 import net.minecraft.network.chat.Component;
 import org.jetbrains.annotations.NotNull;
 
-import javax.annotation.Nonnull;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -114,29 +113,27 @@ public final class RepeatArgumentType<T, U> implements ArgumentType<List<T>> {
 
     public static class Info implements ArgumentTypeInfo<RepeatArgumentType<?, ?>, Template> {
         @Override
-        public void serializeToNetwork(@Nonnull RepeatArgumentType.Template arg, @Nonnull FriendlyByteBuf buf) {
+        public void serializeToNetwork(RepeatArgumentType.Template arg, FriendlyByteBuf buf) {
             buf.writeBoolean(arg.flatten);
             ArgumentUtils.serializeToNetwork(buf, arg.child);
             buf.writeComponent(ArgumentUtils.getMessage(arg.some));
         }
 
-        @Nonnull
         @Override
-        public RepeatArgumentType.Template deserializeFromNetwork(@Nonnull FriendlyByteBuf buf) {
+        public RepeatArgumentType.Template deserializeFromNetwork(FriendlyByteBuf buf) {
             var isList = buf.readBoolean();
             var child = ArgumentUtils.deserialize(buf);
             var message = buf.readComponent();
             return new RepeatArgumentType.Template(this, child, isList, new SimpleCommandExceptionType(message));
         }
 
-        @Nonnull
         @Override
         public RepeatArgumentType.Template unpack(RepeatArgumentType<?, ?> argumentType) {
             return new RepeatArgumentType.Template(this, ArgumentTypeInfos.unpack(argumentType.child), argumentType.flatten, argumentType.some);
         }
 
         @Override
-        public void serializeToJson(@Nonnull RepeatArgumentType.Template arg, @Nonnull JsonObject json) {
+        public void serializeToJson(RepeatArgumentType.Template arg, JsonObject json) {
             json.addProperty("flatten", arg.flatten);
             json.add("child", ArgumentUtils.serializeToJson(arg.child));
             json.addProperty("error", Component.Serializer.toJson(ArgumentUtils.getMessage(arg.some)));
@@ -146,7 +143,6 @@ public final class RepeatArgumentType<T, U> implements ArgumentType<List<T>> {
     public record Template(
         Info info, ArgumentTypeInfo.Template<?> child, boolean flatten, SimpleCommandExceptionType some
     ) implements ArgumentTypeInfo.Template<RepeatArgumentType<?, ?>> {
-        @Nonnull
         @Override
         @SuppressWarnings({ "unchecked", "rawtypes" })
         public RepeatArgumentType<?, ?> instantiate(@NotNull CommandBuildContext commandBuildContext) {
@@ -154,7 +150,6 @@ public final class RepeatArgumentType<T, U> implements ArgumentType<List<T>> {
             return flatten ? RepeatArgumentType.someFlat((ArgumentType) child, some()) : RepeatArgumentType.some(child, some());
         }
 
-        @Nonnull
         @Override
         public ArgumentTypeInfo<RepeatArgumentType<?, ?>, ?> type() {
             return info;

src/main/java/dan200/computercraft/shared/command/builder/CommandBuilder.java

@@ -14,6 +14,7 @@ import com.mojang.brigadier.tree.CommandNode;
 import dan200.computercraft.shared.command.arguments.RepeatArgumentType;
 import net.minecraft.commands.CommandSourceStack;
 
+import javax.annotation.Nullable;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -31,7 +32,7 @@ import static dan200.computercraft.shared.command.builder.HelpingArgumentBuilder
  */
 public class CommandBuilder<S> implements CommandNodeBuilder<S, Command<S>> {
     private final List<ArgumentBuilder<S, ?>> args = new ArrayList<>();
-    private Predicate<S> requires;
+    private @Nullable Predicate<S> requires;
 
     public static CommandBuilder<CommandSourceStack> args() {
         return new CommandBuilder<>();

src/main/java/dan200/computercraft/shared/command/builder/HelpingArgumentBuilder.java

@@ -16,10 +16,11 @@ import net.minecraft.commands.CommandSourceStack;
 import net.minecraft.network.chat.ClickEvent;
 import net.minecraft.network.chat.Component;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.ArrayList;
 import java.util.Collection;
 
+import static dan200.computercraft.core.util.Nullability.assertNonNull;
 import static dan200.computercraft.shared.command.text.ChatHelpers.coloured;
 import static dan200.computercraft.shared.command.text.ChatHelpers.translate;
 
@@ -71,7 +72,7 @@ public final class HelpingArgumentBuilder extends LiteralArgumentBuilder<Command
         return buildImpl(getLiteral().replace('-', '_'), getLiteral());
     }
 
-    private LiteralCommandNode<CommandSourceStack> build(@Nonnull String id, @Nonnull String command) {
+    private LiteralCommandNode<CommandSourceStack> build(String id, String command) {
         return buildImpl(id + "." + getLiteral().replace('-', '_'), command + " " + getLiteral());
     }
 
@@ -120,6 +121,7 @@ public final class HelpingArgumentBuilder extends LiteralArgumentBuilder<Command
     private static final class HelpCommand implements Command<CommandSourceStack> {
         private final String id;
         private final String command;
+        @Nullable
         LiteralCommandNode<CommandSourceStack> node;
 
         private HelpCommand(String id, String command) {
@@ -129,7 +131,7 @@ public final class HelpingArgumentBuilder extends LiteralArgumentBuilder<Command
 
         @Override
         public int run(CommandContext<CommandSourceStack> context) {
-            context.getSource().sendSuccess(getHelp(context, node, id, command), false);
+            context.getSource().sendSuccess(getHelp(context, assertNonNull(node), id, command), false);
             return 0;
         }
     }
@@ -147,7 +149,7 @@ public final class HelpingArgumentBuilder extends LiteralArgumentBuilder<Command
         var dispatcher = context.getSource().getServer().getCommands().getDispatcher();
         CommandNode<CommandSourceStack> temp = new LiteralCommandNode<>("_", null, x -> true, null, null, false);
         temp.addChild(node);
-        var usage = dispatcher.getSmartUsage(temp, context.getSource()).get(node).substring(node.getName().length());
+        var usage = assertNonNull(dispatcher.getSmartUsage(temp, context.getSource()).get(node)).substring(node.getName().length());
 
         var output = Component.literal("")
             .append(coloured("/" + command + usage, HEADER))

src/main/java/dan200/computercraft/shared/command/text/ChatHelpers.java

@@ -12,6 +12,8 @@ import net.minecraft.network.chat.Component;
 import net.minecraft.network.chat.HoverEvent;
 import net.minecraft.network.chat.MutableComponent;
 
+import javax.annotation.Nullable;
+
 /**
  * Various helpers for building chat messages.
  */
@@ -21,7 +23,7 @@ public final class ChatHelpers {
     private ChatHelpers() {
     }
 
-    public static MutableComponent coloured(String text, ChatFormatting colour) {
+    public static MutableComponent coloured(@Nullable String text, ChatFormatting colour) {
         return Component.literal(text == null ? "" : text).withStyle(colour);
     }
 
@@ -30,15 +32,15 @@ public final class ChatHelpers {
         return component;
     }
 
-    public static MutableComponent text(String text) {
+    public static MutableComponent text(@Nullable String text) {
         return Component.literal(text == null ? "" : text);
     }
 
-    public static MutableComponent translate(String text) {
+    public static MutableComponent translate(@Nullable String text) {
         return Component.translatable(text == null ? "" : text);
     }
 
-    public static MutableComponent translate(String text, Object... args) {
+    public static MutableComponent translate(@Nullable String text, Object... args) {
         return Component.translatable(text == null ? "" : text, args);
     }
 
@@ -50,7 +52,7 @@ public final class ChatHelpers {
         return component;
     }
 
-    public static MutableComponent position(BlockPos pos) {
+    public static MutableComponent position(@Nullable BlockPos pos) {
         if (pos == null) return translate("commands.computercraft.generic.no_position");
         return translate("commands.computercraft.generic.position", pos.getX(), pos.getY(), pos.getZ());
     }

src/main/java/dan200/computercraft/shared/command/text/TableBuilder.java

@@ -5,6 +5,7 @@
  */
 package dan200.computercraft.shared.command.text;
 
+import dan200.computercraft.core.util.Nullability;
 import dan200.computercraft.shared.command.CommandUtils;
 import dan200.computercraft.shared.network.client.ChatTableClientMessage;
 import dan200.computercraft.shared.platform.PlatformHelper;
@@ -12,7 +13,6 @@ import net.minecraft.commands.CommandSourceStack;
 import net.minecraft.network.chat.Component;
 import net.minecraft.server.level.ServerPlayer;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.ArrayList;
 import java.util.List;
@@ -20,22 +20,22 @@ import java.util.List;
 public class TableBuilder {
     private final String id;
     private int columns = -1;
-    private final Component[] headers;
+    private final @Nullable Component[] headers;
     private final ArrayList<Component[]> rows = new ArrayList<>();
     private int additional;
 
-    public TableBuilder(@Nonnull String id, @Nonnull Component... headers) {
+    public TableBuilder(String id, Component... headers) {
         this.id = id;
         this.headers = headers;
         columns = headers.length;
     }
 
-    public TableBuilder(@Nonnull String id) {
+    public TableBuilder(String id) {
         this.id = id;
         headers = null;
     }
 
-    public TableBuilder(@Nonnull String id, @Nonnull String... headers) {
+    public TableBuilder(String id, String... headers) {
         this.id = id;
         this.headers = new Component[headers.length];
         columns = headers.length;
@@ -43,7 +43,7 @@ public class TableBuilder {
         for (var i = 0; i < headers.length; i++) this.headers[i] = ChatHelpers.header(headers[i]);
     }
 
-    public void row(@Nonnull Component... row) {
+    public void row(Component... row) {
         if (columns == -1) columns = row.length;
         if (row.length != columns) throw new IllegalArgumentException("Row is the incorrect length");
         rows.add(row);
@@ -78,7 +78,6 @@ public class TableBuilder {
         return headers;
     }
 
-    @Nonnull
     public List<Component[]> getRows() {
         return rows;
     }
@@ -106,7 +105,8 @@ public class TableBuilder {
     public void display(CommandSourceStack source) {
         if (CommandUtils.isPlayer(source)) {
             trim(18);
-            PlatformHelper.get().sendToPlayer(new ChatTableClientMessage(this), (ServerPlayer) source.getEntity());
+            var player = (ServerPlayer) Nullability.assertNonNull(source.getEntity());
+            PlatformHelper.get().sendToPlayer(new ChatTableClientMessage(this), player);
         } else {
             trim(100);
             new ServerTableFormatter(source).display(this);

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

@@ -22,7 +22,6 @@ import net.minecraft.world.level.block.entity.BlockEntityType;
 import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.phys.BlockHitResult;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
 public abstract class BlockGeneric extends BaseEntityBlock {
@@ -35,7 +34,7 @@ public abstract class BlockGeneric extends BaseEntityBlock {
 
     @Override
     @Deprecated
-    public final void onRemove(@Nonnull BlockState block, @Nonnull Level world, @Nonnull BlockPos pos, BlockState replace, boolean bool) {
+    public final void onRemove(BlockState block, Level world, BlockPos pos, BlockState replace, boolean bool) {
         if (block.getBlock() == replace.getBlock()) return;
 
         var tile = world.getBlockEntity(pos);
@@ -44,17 +43,16 @@ public abstract class BlockGeneric extends BaseEntityBlock {
         if (tile instanceof TileGeneric generic) generic.destroy();
     }
 
-    @Nonnull
     @Override
     @Deprecated
-    public final InteractionResult use(@Nonnull BlockState state, Level world, @Nonnull BlockPos pos, @Nonnull Player player, @Nonnull InteractionHand hand, @Nonnull BlockHitResult hit) {
+    public final InteractionResult use(BlockState state, Level world, BlockPos pos, Player player, InteractionHand hand, BlockHitResult hit) {
         var tile = world.getBlockEntity(pos);
         return tile instanceof TileGeneric generic ? generic.onActivate(player, hand, hit) : InteractionResult.PASS;
     }
 
     @Override
     @Deprecated
-    public final void neighborChanged(@Nonnull BlockState state, Level world, @Nonnull BlockPos pos, @Nonnull Block neighbourBlock, @Nonnull BlockPos neighbourPos, boolean isMoving) {
+    public final void neighborChanged(BlockState state, Level world, BlockPos pos, Block neighbourBlock, BlockPos neighbourPos, boolean isMoving) {
         var tile = world.getBlockEntity(pos);
         if (tile instanceof TileGeneric generic) generic.onNeighbourChange(neighbourPos);
     }
@@ -67,21 +65,20 @@ public abstract class BlockGeneric extends BaseEntityBlock {
 
     @Override
     @Deprecated
-    public void tick(@Nonnull BlockState state, ServerLevel world, @Nonnull BlockPos pos, @Nonnull RandomSource rand) {
+    public void tick(BlockState state, ServerLevel world, BlockPos pos, RandomSource rand) {
         var te = world.getBlockEntity(pos);
         if (te instanceof TileGeneric generic) generic.blockTick();
     }
 
     @Nullable
     @Override
-    public BlockEntity newBlockEntity(@Nonnull BlockPos pos, @Nonnull BlockState state) {
+    public BlockEntity newBlockEntity(BlockPos pos, BlockState state) {
         return type.get().create(pos, state);
     }
 
-    @Nonnull
     @Override
     @Deprecated
-    public RenderShape getRenderShape(@Nonnull BlockState state) {
+    public RenderShape getRenderShape(BlockState state) {
         return RenderShape.MODEL;
     }
 }

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

@@ -15,15 +15,13 @@ import net.minecraft.world.item.crafting.CustomRecipe;
 import net.minecraft.world.item.crafting.RecipeSerializer;
 import net.minecraft.world.level.Level;
 
-import javax.annotation.Nonnull;
-
 public final class ColourableRecipe extends CustomRecipe {
     public ColourableRecipe(ResourceLocation id) {
         super(id);
     }
 
     @Override
-    public boolean matches(@Nonnull CraftingContainer inv, @Nonnull Level world) {
+    public boolean matches(CraftingContainer inv, Level world) {
         var hasColourable = false;
         var hasDye = false;
         for (var i = 0; i < inv.getContainerSize(); i++) {
@@ -43,9 +41,8 @@ public final class ColourableRecipe extends CustomRecipe {
         return hasColourable && hasDye;
     }
 
-    @Nonnull
     @Override
-    public ItemStack assemble(@Nonnull CraftingContainer inv) {
+    public ItemStack assemble(CraftingContainer inv) {
         var colourable = ItemStack.EMPTY;
 
         var tracker = new ColourTracker();
@@ -76,7 +73,6 @@ public final class ColourableRecipe extends CustomRecipe {
     }
 
     @Override
-    @Nonnull
     public RecipeSerializer<?> getSerializer() {
         return ModRegistry.RecipeSerializers.DYEABLE_ITEM.get();
     }

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

@@ -16,7 +16,6 @@ import net.minecraft.world.inventory.AbstractContainerMenu;
 import net.minecraft.world.inventory.MenuType;
 import net.minecraft.world.item.ItemStack;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
 public class ContainerHeldItem extends AbstractContainerMenu {
@@ -34,19 +33,17 @@ public class ContainerHeldItem extends AbstractContainerMenu {
         return new ContainerHeldItem(ModRegistry.Menus.PRINTOUT.get(), id, inventory.player, data.getHand());
     }
 
-    @Nonnull
     public ItemStack getStack() {
         return stack;
     }
 
-    @Nonnull
     @Override
-    public ItemStack quickMoveStack(@Nonnull Player player, int slot) {
+    public ItemStack quickMoveStack(Player player, int slot) {
         return ItemStack.EMPTY;
     }
 
     @Override
-    public boolean stillValid(@Nonnull Player player) {
+    public boolean stillValid(Player player) {
         if (!player.isAlive()) return false;
 
         var stack = player.getItemInHand(hand);
@@ -64,7 +61,6 @@ public class ContainerHeldItem extends AbstractContainerMenu {
             this.hand = hand;
         }
 
-        @Nonnull
         @Override
         public Component getDisplayName() {
             return name;
@@ -72,7 +68,7 @@ public class ContainerHeldItem extends AbstractContainerMenu {
 
         @Nullable
         @Override
-        public AbstractContainerMenu createMenu(int id, @Nonnull Inventory inventory, @Nonnull Player player) {
+        public AbstractContainerMenu createMenu(int id, Inventory inventory, Player player) {
             return new ContainerHeldItem(type, id, player, hand);
         }
     }

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

@@ -10,11 +10,10 @@ import net.minecraft.core.BlockPos;
 import net.minecraft.core.Direction;
 import net.minecraft.world.level.Level;
 
-import javax.annotation.Nonnull;
 
 public class DefaultBundledRedstoneProvider implements IBundledRedstoneProvider {
     @Override
-    public int getBundledRedstoneOutput(@Nonnull Level world, @Nonnull BlockPos pos, @Nonnull Direction side) {
+    public int getBundledRedstoneOutput(Level world, BlockPos pos, Direction side) {
         return getDefaultBundledRedstoneOutput(world, pos, side);
     }
 

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

@@ -18,8 +18,6 @@ import net.minecraft.world.level.block.entity.BlockEntityType;
 import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.phys.BlockHitResult;
 
-import javax.annotation.Nonnull;
-
 public abstract class TileGeneric extends BlockEntity {
     public TileGeneric(BlockEntityType<? extends TileGeneric> type, BlockPos pos, BlockState state) {
         super(type, pos, state);
@@ -35,15 +33,14 @@ public abstract class TileGeneric extends BlockEntity {
         getLevel().sendBlockUpdated(pos, state, state, Block.UPDATE_ALL);
     }
 
-    @Nonnull
     public InteractionResult onActivate(Player player, InteractionHand hand, BlockHitResult hit) {
         return InteractionResult.PASS;
     }
 
-    public void onNeighbourChange(@Nonnull BlockPos neighbour) {
+    public void onNeighbourChange(BlockPos neighbour) {
     }
 
-    public void onNeighbourTileEntityChange(@Nonnull BlockPos neighbour) {
+    public void onNeighbourTileEntityChange(BlockPos neighbour) {
     }
 
     protected void blockTick() {
@@ -69,6 +66,6 @@ public abstract class TileGeneric extends BlockEntity {
     }
 
     @Override
-    public void handleUpdateTag(@Nonnull CompoundTag tag) {
+    public void handleUpdateTag(CompoundTag tag) {
     }
 }

src/main/java/dan200/computercraft/shared/computer/apis/CommandAPI.java

@@ -19,9 +19,9 @@ import net.minecraft.core.BlockPos;
 import net.minecraft.core.Registry;
 import net.minecraft.resources.ResourceKey;
 import net.minecraft.resources.ResourceLocation;
+import net.minecraft.server.level.ServerLevel;
 import net.minecraft.world.level.Level;
 
-import javax.annotation.Nonnull;
 import java.util.*;
 
 /**
@@ -243,9 +243,8 @@ public class CommandAPI implements ILuaAPI {
         return getBlockInfo(level, position);
     }
 
-    @Nonnull
+    private Level getLevel(Optional<String> id) throws LuaException {
-    private Level getLevel(@Nonnull Optional<String> id) throws LuaException {
+        var currentLevel = (ServerLevel) computer.getLevel();
-        var currentLevel = computer.getLevel();
         if (currentLevel == null) throw new LuaException("No world exists");
 
         if (!id.isPresent()) return currentLevel;

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

@@ -22,7 +22,6 @@ import net.minecraft.world.level.block.state.properties.BlockStateProperties;
 import net.minecraft.world.level.block.state.properties.DirectionProperty;
 import net.minecraft.world.level.block.state.properties.EnumProperty;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
 public class BlockComputer<T extends TileComputer> extends BlockComputerBase<T> {
@@ -48,21 +47,18 @@ public class BlockComputer<T extends TileComputer> extends BlockComputerBase<T>
         return defaultBlockState().setValue(FACING, placement.getHorizontalDirection().getOpposite());
     }
 
-    @Nonnull
     @Override
     @Deprecated
     public BlockState mirror(BlockState state, Mirror mirrorIn) {
         return state.rotate(mirrorIn.getRotation(state.getValue(FACING)));
     }
 
-    @Nonnull
     @Override
     @Deprecated
     public BlockState rotate(BlockState state, Rotation rot) {
         return state.setValue(FACING, rot.rotate(state.getValue(FACING)));
     }
 
-    @Nonnull
     @Override
     protected ItemStack getItem(TileComputerBase tile) {
         return tile instanceof TileComputer ? ComputerItemFactory.create((TileComputer) tile) : ItemStack.EMPTY;

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

@@ -32,7 +32,6 @@ import net.minecraft.world.level.storage.loot.parameters.LootContextParams;
 import net.minecraft.world.phys.HitResult;
 import net.minecraft.world.phys.Vec3;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
 public abstract class BlockComputerBase<T extends TileComputerBase> extends BlockGeneric implements IBundledRedstoneBlock {
@@ -50,7 +49,7 @@ public abstract class BlockComputerBase<T extends TileComputerBase> extends Bloc
 
     @Override
     @Deprecated
-    public void onPlace(@Nonnull BlockState state, @Nonnull Level world, @Nonnull BlockPos pos, @Nonnull BlockState oldState, boolean isMoving) {
+    public void onPlace(BlockState state, Level world, BlockPos pos, BlockState oldState, boolean isMoving) {
         super.onPlace(state, world, pos, oldState, isMoving);
 
         var tile = world.getBlockEntity(pos);
@@ -59,13 +58,13 @@ public abstract class BlockComputerBase<T extends TileComputerBase> extends Bloc
 
     @Override
     @Deprecated
-    public boolean isSignalSource(@Nonnull BlockState state) {
+    public boolean isSignalSource(BlockState state) {
         return true;
     }
 
     @Override
     @Deprecated
-    public int getDirectSignal(@Nonnull BlockState state, BlockGetter world, @Nonnull BlockPos pos, @Nonnull Direction incomingSide) {
+    public int getDirectSignal(BlockState state, BlockGetter world, BlockPos pos, Direction incomingSide) {
         var entity = world.getBlockEntity(pos);
         if (!(entity instanceof TileComputerBase computerEntity)) return 0;
 
@@ -76,7 +75,6 @@ public abstract class BlockComputerBase<T extends TileComputerBase> extends Bloc
         return computer.getRedstoneOutput(localSide);
     }
 
-    @Nonnull
     protected abstract ItemStack getItem(TileComputerBase tile);
 
     public ComputerFamily getFamily() {
@@ -85,7 +83,7 @@ public abstract class BlockComputerBase<T extends TileComputerBase> extends Bloc
 
     @Override
     @Deprecated
-    public int getSignal(@Nonnull BlockState state, @Nonnull BlockGetter world, @Nonnull BlockPos pos, @Nonnull Direction incomingSide) {
+    public int getSignal(BlockState state, BlockGetter world, BlockPos pos, Direction incomingSide) {
         return getDirectSignal(state, world, pos, incomingSide);
     }
 
@@ -106,7 +104,6 @@ public abstract class BlockComputerBase<T extends TileComputerBase> extends Bloc
         return computer.getBundledRedstoneOutput(localSide);
     }
 
-    @Nonnull
     @Override
     public ItemStack getCloneItemStack(BlockState state, HitResult target, BlockGetter world, BlockPos pos, Player player) {
         var tile = world.getBlockEntity(pos);
@@ -119,14 +116,14 @@ public abstract class BlockComputerBase<T extends TileComputerBase> extends Bloc
     }
 
     @Override
-    public void playerDestroy(@Nonnull Level world, Player player, @Nonnull BlockPos pos, @Nonnull BlockState state, @Nullable BlockEntity tile, @Nonnull ItemStack tool) {
+    public void playerDestroy(Level world, Player player, BlockPos pos, BlockState state, @Nullable BlockEntity tile, ItemStack tool) {
         // Don't drop blocks here - see onBlockHarvested.
         player.awardStat(Stats.BLOCK_MINED.get(this));
         player.causeFoodExhaustion(0.005F);
     }
 
     @Override
-    public void playerWillDestroy(@Nonnull Level world, @Nonnull BlockPos pos, @Nonnull BlockState state, @Nonnull Player player) {
+    public void playerWillDestroy(Level world, BlockPos pos, BlockState state, Player player) {
         if (!(world instanceof ServerLevel serverWorld)) return;
 
         // We drop the item here instead of doing it in the harvest method, as we should
@@ -150,7 +147,7 @@ public abstract class BlockComputerBase<T extends TileComputerBase> extends Bloc
     }
 
     @Override
-    public void setPlacedBy(@Nonnull Level world, @Nonnull BlockPos pos, @Nonnull BlockState state, LivingEntity placer, @Nonnull ItemStack stack) {
+    public void setPlacedBy(Level world, BlockPos pos, BlockState state, @Nullable LivingEntity placer, ItemStack stack) {
         super.setPlacedBy(world, pos, state, placer, stack);
 
         var tile = world.getBlockEntity(pos);
@@ -171,7 +168,7 @@ public abstract class BlockComputerBase<T extends TileComputerBase> extends Bloc
 
     @Override
     @Nullable
-    public <U extends BlockEntity> BlockEntityTicker<U> getTicker(@Nonnull Level level, @Nonnull BlockState state, @Nonnull BlockEntityType<U> type) {
+    public <U extends BlockEntity> BlockEntityTicker<U> getTicker(Level level, BlockState state, BlockEntityType<U> type) {
         return level.isClientSide ? null : BaseEntityBlock.createTickerHelper(type, this.type.get(), serverTicker);
     }
 }

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

@@ -9,7 +9,6 @@ import dan200.computercraft.api.lua.LuaFunction;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.core.apis.OSAPI;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
 /**
@@ -29,7 +28,6 @@ public class ComputerPeripheral implements IPeripheral {
         this.owner = owner;
     }
 
-    @Nonnull
     @Override
     public String getType() {
         return type;
@@ -111,11 +109,10 @@ public class ComputerPeripheral implements IPeripheral {
     }
 
     @Override
-    public boolean equals(IPeripheral other) {
+    public boolean equals(@Nullable IPeripheral other) {
         return other instanceof ComputerPeripheral computerPeripheral && owner == computerPeripheral.owner;
     }
 
-    @Nonnull
     @Override
     public Object getTarget() {
         return owner;

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

@@ -7,14 +7,17 @@ package dan200.computercraft.shared.computer.blocks;
 
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 
+import javax.annotation.Nullable;
+
 public interface IComputerTile {
     int getComputerID();
 
     void setComputerID(int id);
 
+    @Nullable
     String getLabel();
 
-    void setLabel(String label);
+    void setLabel(@Nullable String label);
 
     ComputerFamily getFamily();
 }

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

@@ -21,7 +21,6 @@ import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.phys.Vec2;
 import net.minecraft.world.phys.Vec3;
 
-import javax.annotation.Nonnull;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -42,7 +41,7 @@ public class TileCommandComputer extends TileComputer {
         }
 
         @Override
-        public void sendSystemMessage(@Nonnull Component textComponent) {
+        public void sendSystemMessage(Component textComponent) {
             output.put(output.size() + 1, textComponent.getString());
         }
 

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

@@ -22,11 +22,10 @@ import net.minecraft.world.inventory.AbstractContainerMenu;
 import net.minecraft.world.level.block.entity.BlockEntityType;
 import net.minecraft.world.level.block.state.BlockState;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
 public class TileComputer extends TileComputerBase {
-    private IPeripheral peripheral;
+    private @Nullable IPeripheral peripheral;
 
     public TileComputer(BlockEntityType<? extends TileComputer> type, BlockPos pos, BlockState state, ComputerFamily family) {
         super(type, pos, state, family);
@@ -35,12 +34,11 @@ public class TileComputer extends TileComputerBase {
     @Override
     protected ServerComputer createComputer(int id) {
         var family = getFamily();
-        var computer = new ServerComputer(
+        return new ServerComputer(
-            (ServerLevel) getLevel(), id, label, family,
+            (ServerLevel) getLevel(), getBlockPos(), id, label,
-            ComputerCraft.computerTermWidth, ComputerCraft.computerTermHeight
+            family, ComputerCraft.computerTermWidth,
+            ComputerCraft.computerTermHeight
         );
-        computer.setPosition(getBlockPos());
-        return computer;
     }
 
     protected boolean isUsableByPlayer(Player player) {
@@ -71,7 +69,7 @@ public class TileComputer extends TileComputerBase {
 
     @Nullable
     @Override
-    public AbstractContainerMenu createMenu(int id, @Nonnull Inventory inventory, @Nonnull Player player) {
+    public AbstractContainerMenu createMenu(int id, Inventory inventory, Player player) {
         return new ComputerMenuWithoutInventory(ModRegistry.Menus.COMPUTER.get(), id, inventory, this::isUsableByPlayer, createServerComputer(), getFamily());
     }
 

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

@@ -36,7 +36,6 @@ import net.minecraft.world.level.block.entity.BlockEntityType;
 import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.phys.BlockHitResult;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.Objects;
 
@@ -47,7 +46,7 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
 
     private int instanceID = -1;
     private int computerID = -1;
-    protected String label = null;
+    protected @Nullable String label = null;
     private boolean on = false;
     boolean startOn = false;
     private boolean fresh = false;
@@ -100,7 +99,6 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
         return super.isUsable(player) && BaseContainerBlockEntity.canUnlock(player, lockCode, getDisplayName());
     }
 
-    @Nonnull
     @Override
     public InteractionResult onActivate(Player player, InteractionHand hand, BlockHitResult hit) {
         var currentItem = player.getItemInHand(hand);
@@ -128,12 +126,12 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
     }
 
     @Override
-    public void onNeighbourChange(@Nonnull BlockPos neighbour) {
+    public void onNeighbourChange(BlockPos neighbour) {
         updateInputAt(neighbour);
     }
 
     @Override
-    public void onNeighbourTileEntityChange(@Nonnull BlockPos neighbour) {
+    public void onNeighbourTileEntityChange(BlockPos neighbour) {
         updateInputAt(neighbour);
     }
 
@@ -174,7 +172,7 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
     protected abstract void updateBlockState(ComputerState newState);
 
     @Override
-    public void saveAdditional(@Nonnull CompoundTag nbt) {
+    public void saveAdditional(CompoundTag nbt) {
         // Save ID, label and power state
         if (computerID >= 0) nbt.putInt(NBT_ID, computerID);
         if (label != null) nbt.putString(NBT_LABEL, label);
@@ -186,7 +184,7 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
     }
 
     @Override
-    public void load(@Nonnull CompoundTag nbt) {
+    public void load(CompoundTag nbt) {
         super.load(nbt);
 
         // Load ID, label and power state
@@ -211,7 +209,7 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
         return localSide;
     }
 
-    private void updateRedstoneInput(@Nonnull ServerComputer computer, Direction dir, BlockPos targetPos) {
+    private void updateRedstoneInput(ServerComputer computer, Direction dir, BlockPos targetPos) {
         var offsetSide = dir.getOpposite();
         var localDir = remapToLocalSide(dir);
 
@@ -219,7 +217,7 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
         computer.setBundledRedstoneInput(localDir, BundledRedstone.getOutput(getLevel(), targetPos, offsetSide));
     }
 
-    private void refreshPeripheral(@Nonnull ServerComputer computer, Direction dir) {
+    private void refreshPeripheral(ServerComputer computer, Direction dir) {
         invalidSides &= ~(1 << dir.ordinal());
 
         var localDir = remapToLocalSide(dir);
@@ -243,7 +241,7 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
      *
      * @param computer The current computer instance.
      */
-    private void updateInputsImmediately(@Nonnull ServerComputer computer) {
+    private void updateInputsImmediately(ServerComputer computer) {
         var pos = getBlockPos();
         for (var dir : DirectionUtil.FACINGS) {
             updateRedstoneInput(computer, dir, pos.relative(dir));
@@ -251,7 +249,7 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
         }
     }
 
-    private void updateInputAt(@Nonnull BlockPos neighbour) {
+    private void updateInputAt(BlockPos neighbour) {
         var computer = getServerComputer();
         if (computer == null) return;
 
@@ -289,7 +287,7 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
     }
 
     @Override
-    public final String getLabel() {
+    public final @Nullable String getLabel() {
         return label;
     }
 
@@ -302,7 +300,7 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
     }
 
     @Override
-    public final void setLabel(String label) {
+    public final void setLabel(@Nullable String label) {
         if (getLevel().isClientSide || Objects.equals(this.label, label)) return;
 
         this.label = label;
@@ -316,13 +314,13 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
         return family;
     }
 
-    @Nonnull
     public final ServerComputer createServerComputer() {
-        if (getLevel().isClientSide) throw new IllegalStateException("Cannot access server computer on the client.");
+        var server = getLevel().getServer();
+        if (server == null) throw new IllegalStateException("Cannot access server computer on the client.");
 
         var changed = false;
 
-        var computer = ServerContext.get(getLevel().getServer()).registry().get(instanceID);
+        var computer = ServerContext.get(server).registry().get(instanceID);
         if (computer == null) {
             if (computerID < 0) {
                 computerID = ComputerCraftAPI.createUniqueNumberedSaveDir(level, IDAssigner.COMPUTER);
@@ -341,18 +339,16 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
 
     @Nullable
     public ServerComputer getServerComputer() {
-        return getLevel().isClientSide ? null : ServerContext.get(getLevel().getServer()).registry().get(instanceID);
+        return getLevel().isClientSide || getLevel().getServer() == null ? null : ServerContext.get(getLevel().getServer()).registry().get(instanceID);
     }
 
     // Networking stuff
 
-    @Nonnull
     @Override
     public final ClientboundBlockEntityDataPacket getUpdatePacket() {
         return ClientboundBlockEntityDataPacket.create(this);
     }
 
-    @Nonnull
     @Override
     public CompoundTag getUpdateTag() {
         // We need this for pick block on the client side.
@@ -363,7 +359,7 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
     }
 
     @Override
-    public void handleUpdateTag(@Nonnull CompoundTag nbt) {
+    public void handleUpdateTag(CompoundTag nbt) {
         label = nbt.contains(NBT_LABEL) ? nbt.getString(NBT_LABEL) : null;
         computerID = nbt.contains(NBT_ID) ? nbt.getInt(NBT_ID) : -1;
     }
@@ -382,7 +378,6 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
         copy.instanceID = -1;
     }
 
-    @Nonnull
     @Override
     public Component getName() {
         return hasCustomName()
@@ -401,7 +396,6 @@ public abstract class TileComputerBase extends TileGeneric implements IComputerT
         return hasCustomName() ? Component.literal(label) : null;
     }
 
-    @Nonnull
     @Override
     public Component getDisplayName() {
         return Nameable.super.getDisplayName();

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

@@ -7,8 +7,6 @@ package dan200.computercraft.shared.computer.core;
 
 import net.minecraft.util.StringRepresentable;
 
-import javax.annotation.Nonnull;
-
 public enum ComputerState implements StringRepresentable {
     OFF("off", ""),
     ON("on", "_on"),
@@ -22,7 +20,6 @@ public enum ComputerState implements StringRepresentable {
         this.texture = texture;
     }
 
-    @Nonnull
     @Override
     public String getSerializedName() {
         return name;
@@ -33,7 +30,6 @@ public enum ComputerState implements StringRepresentable {
         return name;
     }
 
-    @Nonnull
     public String getTexture() {
         return texture;
     }

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

@@ -19,7 +19,6 @@ import net.minecraft.server.packs.resources.ResourceManager;
 import net.minecraft.server.packs.resources.SimplePreparableReloadListener;
 import net.minecraft.util.profiling.ProfilerFiller;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.io.IOException;
 import java.nio.channels.Channels;
@@ -108,7 +107,7 @@ public final class ResourceMount implements IMount {
         }
     }
 
-    private FileEntry get(String path) {
+    private @Nullable FileEntry get(String path) {
         var lastEntry = root;
         var lastIndex = 0;
 
@@ -150,18 +149,18 @@ public final class ResourceMount implements IMount {
     }
 
     @Override
-    public boolean exists(@Nonnull String path) {
+    public boolean exists(String path) {
         return get(path) != null;
     }
 
     @Override
-    public boolean isDirectory(@Nonnull String path) {
+    public boolean isDirectory(String path) {
         var file = get(path);
         return file != null && file.isDirectory();
     }
 
     @Override
-    public void list(@Nonnull String path, @Nonnull List<String> contents) throws IOException {
+    public void list(String path, List<String> contents) throws IOException {
         var file = get(path);
         if (file == null || !file.isDirectory()) throw new IOException("/" + path + ": Not a directory");
 
@@ -169,7 +168,7 @@ public final class ResourceMount implements IMount {
     }
 
     @Override
-    public long getSize(@Nonnull String path) throws IOException {
+    public long getSize(String path) throws IOException {
         var file = get(path);
         if (file != null) {
             if (file.size != -1) return file.size;
@@ -197,9 +196,8 @@ public final class ResourceMount implements IMount {
         throw new IOException("/" + path + ": No such file");
     }
 
-    @Nonnull
     @Override
-    public ReadableByteChannel openForRead(@Nonnull String path) throws IOException {
+    public ReadableByteChannel openForRead(String path) throws IOException {
         var file = get(path);
         if (file != null && !file.isDirectory()) {
             var contents = CONTENTS_CACHE.getIfPresent(file);
@@ -226,6 +224,7 @@ public final class ResourceMount implements IMount {
 
     private static class FileEntry {
         final ResourceLocation identifier;
+        @Nullable
         Map<String, FileEntry> children;
         long size = -1;
 
@@ -243,13 +242,12 @@ public final class ResourceMount implements IMount {
     }
 
     /**
-     * A {@link PreparableReloadListener} which reloads any associated mounts and correctly updates the resource manager
+     * A {@link SimplePreparableReloadListener} which reloads any associated mounts and correctly updates the resource manager
      * they point to.
      */
     public static final SimplePreparableReloadListener<Void> RELOAD_LISTENER = new SimplePreparableReloadListener<>() {
-        @Nonnull
         @Override
-        protected Void prepare(@Nonnull ResourceManager manager, @Nonnull ProfilerFiller profiler) {
+        protected Void prepare(ResourceManager manager, ProfilerFiller profiler) {
             profiler.push("Reloading ComputerCraft mounts");
             try {
                 for (var mount : MOUNT_CACHE.values()) mount.load(manager);
@@ -261,7 +259,7 @@ public final class ResourceMount implements IMount {
         }
 
         @Override
-        protected void apply(@Nonnull Void result, @Nonnull ResourceManager manager, @Nonnull ProfilerFiller profiler) {
+        protected void apply(Void result, ResourceManager manager, ProfilerFiller profiler) {
         }
     };
 }

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

@@ -26,6 +26,7 @@ import net.minecraft.core.BlockPos;
 import net.minecraft.server.level.ServerLevel;
 import net.minecraft.world.inventory.AbstractContainerMenu;
 
+import javax.annotation.Nullable;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Function;
 
@@ -45,8 +46,11 @@ public class ServerComputer implements InputHandler, ComputerEnvironment {
     private boolean changedLastFrame;
     private int ticksSincePing;
 
-    public ServerComputer(ServerLevel level, int computerID, String label, ComputerFamily family, int terminalWidth, int terminalHeight) {
+    public ServerComputer(
+        ServerLevel level, BlockPos position, int computerID, @Nullable String label, ComputerFamily family, int terminalWidth, int terminalHeight
+    ) {
         this.level = level;
+        this.position = position;
         this.family = family;
 
         var context = ServerContext.get(level.getServer());
@@ -155,7 +159,7 @@ public class ServerComputer implements InputHandler, ComputerEnvironment {
         return computer.getID();
     }
 
-    public String getLabel() {
+    public @Nullable String getLabel() {
         return computer.getLabel();
     }
 
@@ -187,7 +191,7 @@ public class ServerComputer implements InputHandler, ComputerEnvironment {
     }
 
     @Override
-    public void queueEvent(String event, Object[] arguments) {
+    public void queueEvent(String event, @Nullable Object[] arguments) {
         // Queue event
         computer.queueEvent(event, arguments);
     }
@@ -212,15 +216,16 @@ public class ServerComputer implements InputHandler, ComputerEnvironment {
         computer.addApi(api);
     }
 
-    public void setPeripheral(ComputerSide side, IPeripheral peripheral) {
+    public void setPeripheral(ComputerSide side, @Nullable IPeripheral peripheral) {
         computer.getEnvironment().setPeripheral(side, peripheral);
     }
 
+    @Nullable
     public IPeripheral getPeripheral(ComputerSide side) {
         return computer.getEnvironment().getPeripheral(side);
     }
 
-    public void setLabel(String label) {
+    public void setLabel(@Nullable String label) {
         computer.setLabel(label);
     }
 
@@ -240,7 +245,7 @@ public class ServerComputer implements InputHandler, ComputerEnvironment {
     }
 
     @Override
-    public IWritableMount createRootMount() {
+    public @Nullable IWritableMount createRootMount() {
         return ComputerCraftAPI.createSaveDirMount(level, "computer/" + computer.getID(), ComputerCraft.computerSpaceLimit);
     }
 }

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

@@ -24,7 +24,6 @@ import net.minecraft.server.MinecraftServer;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.level.storage.LevelResource;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.io.InputStream;
 import java.nio.file.Path;
@@ -180,23 +179,21 @@ public final class ServerContext {
 
     private record Environment(MinecraftServer server) implements GlobalEnvironment {
         @Override
-        public IMount createResourceMount(String domain, String subPath) {
+        public @Nullable IMount createResourceMount(String domain, String subPath) {
             return ComputerCraftAPI.createResourceMount(domain, subPath);
         }
 
         @Override
-        public InputStream createResourceFile(String domain, String subPath) {
+        public @Nullable InputStream createResourceFile(String domain, String subPath) {
             return ComputerCraftAPIImpl.getResourceFile(server, domain, subPath);
         }
 
-        @Nonnull
         @Override
         public String getHostString() {
             var version = SharedConstants.getCurrentVersion().getName();
             return String.format("ComputerCraft %s (Minecraft %s)", ComputerCraftAPI.getInstalledVersion(), version);
         }
 
-        @Nonnull
         @Override
         public String getUserAgent() {
             return ComputerCraft.MOD_ID + "/" + ComputerCraftAPI.getInstalledVersion();

src/main/java/dan200/computercraft/shared/computer/inventory/ComputerMenuWithoutInventory.java

@@ -14,7 +14,6 @@ import net.minecraft.world.entity.player.Player;
 import net.minecraft.world.inventory.MenuType;
 import net.minecraft.world.item.ItemStack;
 
-import javax.annotation.Nonnull;
 import java.util.function.Predicate;
 
 /**
@@ -40,9 +39,8 @@ public class ComputerMenuWithoutInventory extends ContainerComputerBase {
         for (var i = 0; i < 9; i++) addSlot(new InvisibleSlot(player, i));
     }
 
-    @Nonnull
     @Override
-    public ItemStack quickMoveStack(@Nonnull Player player, int slot) {
+    public ItemStack quickMoveStack(Player player, int slot) {
         return ItemStack.EMPTY;
     }
 }

src/main/java/dan200/computercraft/shared/computer/inventory/ContainerComputerBase.java

@@ -22,7 +22,6 @@ import net.minecraft.world.inventory.MenuType;
 import net.minecraft.world.inventory.SimpleContainerData;
 import net.minecraft.world.item.ItemStack;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.function.Predicate;
 
@@ -51,15 +50,14 @@ public abstract class ContainerComputerBase extends AbstractContainerMenu implem
         this.computer = computer;
         input = computer == null ? null : new ServerInputState<>(this);
         terminal = containerData == null ? null : containerData.terminal().create();
-        displayStack = containerData == null ? null : containerData.displayStack();
+        displayStack = containerData == null ? ItemStack.EMPTY : containerData.displayStack();
     }
 
     @Override
-    public boolean stillValid(@Nonnull Player player) {
+    public boolean stillValid(Player player) {
         return canUse.test(player);
     }
 
-    @Nonnull
     public ComputerFamily getFamily() {
         return family;
     }
@@ -98,7 +96,7 @@ public abstract class ContainerComputerBase extends AbstractContainerMenu implem
     }
 
     @Override
-    public void removed(@Nonnull Player player) {
+    public void removed(Player player) {
         super.removed(player);
         if (input != null) input.close();
     }
@@ -108,7 +106,6 @@ public abstract class ContainerComputerBase extends AbstractContainerMenu implem
      *
      * @return The current stack.
      */
-    @Nonnull
     public ItemStack getDisplayStack() {
         return displayStack;
     }

src/main/java/dan200/computercraft/shared/computer/inventory/ContainerViewComputer.java

@@ -14,7 +14,6 @@ import dan200.computercraft.shared.network.container.ComputerContainerData;
 import net.minecraft.world.entity.player.Inventory;
 import net.minecraft.world.entity.player.Player;
 
-import javax.annotation.Nonnull;
 
 public class ContainerViewComputer extends ComputerMenuWithoutInventory {
     public ContainerViewComputer(int id, Inventory player, ServerComputer computer) {
@@ -25,7 +24,7 @@ public class ContainerViewComputer extends ComputerMenuWithoutInventory {
         super(ModRegistry.Menus.VIEW_COMPUTER.get(), id, player, data);
     }
 
-    private static boolean canInteractWith(@Nonnull ServerComputer computer, @Nonnull Player player) {
+    private static boolean canInteractWith(ServerComputer computer, Player player) {
         // If this computer no longer exists then discard it.
         if (ServerContext.get(computer.getLevel().getServer()).registry().get(computer.getInstanceID()) != computer) {
             return false;

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

@@ -10,19 +10,17 @@ import dan200.computercraft.shared.computer.blocks.TileComputer;
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 import net.minecraft.world.item.ItemStack;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 public final class ComputerItemFactory {
     private ComputerItemFactory() {
     }
 
-    @Nonnull
     public static ItemStack create(TileComputer tile) {
         return create(tile.getComputerID(), tile.getLabel(), tile.getFamily());
     }
 
-    @Nonnull
+    public static ItemStack create(int id, @Nullable String label, ComputerFamily family) {
-    public static ItemStack create(int id, String label, ComputerFamily family) {
         return switch (family) {
             case NORMAL -> ModRegistry.Items.COMPUTER_NORMAL.get().create(id, label);
             case ADVANCED -> ModRegistry.Items.COMPUTER_ADVANCED.get().create(id, label);

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

@@ -8,21 +8,21 @@ package dan200.computercraft.shared.computer.items;
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 import net.minecraft.world.item.ItemStack;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 public interface IComputerItem {
     String NBT_ID = "ComputerId";
 
-    default int getComputerID(@Nonnull ItemStack stack) {
+    default int getComputerID(ItemStack stack) {
         var nbt = stack.getTag();
         return nbt != null && nbt.contains(NBT_ID) ? nbt.getInt(NBT_ID) : -1;
     }
 
-    default String getLabel(@Nonnull ItemStack stack) {
+    default @Nullable String getLabel(ItemStack stack) {
         return stack.hasCustomHoverName() ? stack.getHoverName().getString() : null;
     }
 
     ComputerFamily getFamily();
 
-    ItemStack withFamily(@Nonnull ItemStack stack, @Nonnull ComputerFamily family);
+    ItemStack withFamily(ItemStack stack, ComputerFamily family);
 }

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

@@ -10,14 +10,14 @@ import dan200.computercraft.shared.computer.core.ComputerFamily;
 import net.minecraft.network.chat.Component;
 import net.minecraft.world.item.ItemStack;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 public class ItemComputer extends ItemComputerBase {
     public ItemComputer(BlockComputer<?> block, Properties settings) {
         super(block, settings);
     }
 
-    public ItemStack create(int id, String label) {
+    public ItemStack create(int id, @Nullable String label) {
         var result = new ItemStack(this);
         if (id >= 0) result.getOrCreateTag().putInt(NBT_ID, id);
         if (label != null) result.setHoverName(Component.literal(label));
@@ -25,7 +25,7 @@ public class ItemComputer extends ItemComputerBase {
     }
 
     @Override
-    public ItemStack withFamily(@Nonnull ItemStack stack, @Nonnull ComputerFamily family) {
+    public ItemStack withFamily(ItemStack stack, ComputerFamily family) {
         var result = ComputerItemFactory.create(getComputerID(stack), null, family);
         if (stack.hasCustomHoverName()) result.setHoverName(stack.getHoverName());
         return result;

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

@@ -18,7 +18,6 @@ import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.TooltipFlag;
 import net.minecraft.world.level.Level;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.List;
 
@@ -31,7 +30,7 @@ public abstract class ItemComputerBase extends BlockItem implements IComputerIte
     }
 
     @Override
-    public void appendHoverText(@Nonnull ItemStack stack, @Nullable Level world, @Nonnull List<Component> list, @Nonnull TooltipFlag options) {
+    public void appendHoverText(ItemStack stack, @Nullable Level world, List<Component> list, TooltipFlag options) {
         if (options.isAdvanced() || getLabel(stack) == null) {
             var id = getComputerID(stack);
             if (id >= 0) {
@@ -42,7 +41,7 @@ public abstract class ItemComputerBase extends BlockItem implements IComputerIte
     }
 
     @Override
-    public String getLabel(@Nonnull ItemStack stack) {
+    public @Nullable String getLabel(ItemStack stack) {
         return IComputerItem.super.getLabel(stack);
     }
 
@@ -54,7 +53,7 @@ public abstract class ItemComputerBase extends BlockItem implements IComputerIte
     // IMedia implementation
 
     @Override
-    public boolean setLabel(@Nonnull ItemStack stack, String label) {
+    public boolean setLabel(ItemStack stack, @Nullable String label) {
         if (label != null) {
             stack.setHoverName(Component.literal(label));
         } else {
@@ -64,7 +63,7 @@ public abstract class ItemComputerBase extends BlockItem implements IComputerIte
     }
 
     @Override
-    public IMount createDataMount(@Nonnull ItemStack stack, @Nonnull Level world) {
+    public @Nullable IMount createDataMount(ItemStack stack, Level world) {
         var family = getFamily();
         if (family != ComputerFamily.COMMAND) {
             var id = getComputerID(stack);

src/main/java/dan200/computercraft/shared/computer/menu/ServerInputHandler.java

@@ -11,7 +11,6 @@ import dan200.computercraft.shared.computer.upload.FileUpload;
 import dan200.computercraft.shared.network.server.ComputerServerMessage;
 import net.minecraft.server.level.ServerPlayer;
 
-import javax.annotation.Nonnull;
 import java.util.List;
 import java.util.UUID;
 
@@ -29,7 +28,7 @@ public interface ServerInputHandler extends InputHandler {
      * @param uploadId The unique ID of this upload.
      * @param files    The files to upload.
      */
-    void startUpload(@Nonnull UUID uploadId, @Nonnull List<FileUpload> files);
+    void startUpload(UUID uploadId, List<FileUpload> files);
 
     /**
      * Append more data to partially uploaded files.
@@ -37,7 +36,7 @@ public interface ServerInputHandler extends InputHandler {
      * @param uploadId The unique ID of this upload.
      * @param slices   Additional parts of file data to upload.
      */
-    void continueUpload(@Nonnull UUID uploadId, @Nonnull List<FileSlice> slices);
+    void continueUpload(UUID uploadId, List<FileSlice> slices);
 
     /**
      * Finish off an upload. This either writes the uploaded files or informs the user that files will be overwritten.
@@ -45,5 +44,5 @@ public interface ServerInputHandler extends InputHandler {
      * @param uploader The player uploading files.
      * @param uploadId The unique ID of this upload.
      */
-    void finishUpload(@Nonnull ServerPlayer uploader, @Nonnull UUID uploadId);
+    void finishUpload(ServerPlayer uploader, UUID uploadId);
 }

src/main/java/dan200/computercraft/shared/computer/recipe/ComputerConvertRecipe.java

@@ -14,8 +14,6 @@ import net.minecraft.world.item.crafting.Ingredient;
 import net.minecraft.world.item.crafting.ShapedRecipe;
 import net.minecraft.world.level.Level;
 
-import javax.annotation.Nonnull;
-
 /**
  * Represents a recipe which converts a computer from one form into another.
  */
@@ -27,11 +25,10 @@ public abstract class ComputerConvertRecipe extends ShapedRecipe {
         this.group = group;
     }
 
-    @Nonnull
+    protected abstract ItemStack convert(IComputerItem item, ItemStack stack);
-    protected abstract ItemStack convert(@Nonnull IComputerItem item, @Nonnull ItemStack stack);
 
     @Override
-    public boolean matches(@Nonnull CraftingContainer inventory, @Nonnull Level world) {
+    public boolean matches(CraftingContainer inventory, Level world) {
         if (!super.matches(inventory, world)) return false;
 
         for (var i = 0; i < inventory.getContainerSize(); i++) {
@@ -41,9 +38,8 @@ public abstract class ComputerConvertRecipe extends ShapedRecipe {
         return false;
     }
 
-    @Nonnull
     @Override
-    public ItemStack assemble(@Nonnull CraftingContainer inventory) {
+    public ItemStack assemble(CraftingContainer inventory) {
         // Find our computer item and convert it.
         for (var i = 0; i < inventory.getContainerSize(); i++) {
             var stack = inventory.getItem(i);
@@ -53,7 +49,6 @@ public abstract class ComputerConvertRecipe extends ShapedRecipe {
         return ItemStack.EMPTY;
     }
 
-    @Nonnull
     @Override
     public String getGroup() {
         return group;

src/main/java/dan200/computercraft/shared/computer/recipe/ComputerFamilyRecipe.java

@@ -16,8 +16,6 @@ import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.crafting.Ingredient;
 import net.minecraft.world.item.crafting.RecipeSerializer;
 
-import javax.annotation.Nonnull;
-
 public abstract class ComputerFamilyRecipe extends ComputerConvertRecipe {
     private final ComputerFamily family;
 
@@ -33,9 +31,8 @@ public abstract class ComputerFamilyRecipe extends ComputerConvertRecipe {
     public abstract static class Serializer<T extends ComputerFamilyRecipe> implements RecipeSerializer<T> {
         protected abstract T create(ResourceLocation identifier, String group, int width, int height, NonNullList<Ingredient> ingredients, ItemStack result, ComputerFamily family);
 
-        @Nonnull
         @Override
-        public T fromJson(@Nonnull ResourceLocation identifier, @Nonnull JsonObject json) {
+        public T fromJson(ResourceLocation identifier, JsonObject json) {
             var group = GsonHelper.getAsString(json, "group", "");
             var family = RecipeUtil.getFamily(json, "family");
 
@@ -45,9 +42,8 @@ public abstract class ComputerFamilyRecipe extends ComputerConvertRecipe {
             return create(identifier, group, template.width(), template.height(), template.ingredients(), result, family);
         }
 
-        @Nonnull
         @Override
-        public T fromNetwork(@Nonnull ResourceLocation identifier, @Nonnull FriendlyByteBuf buf) {
+        public T fromNetwork(ResourceLocation identifier, FriendlyByteBuf buf) {
             var width = buf.readVarInt();
             var height = buf.readVarInt();
             var group = buf.readUtf(Short.MAX_VALUE);
@@ -61,7 +57,7 @@ public abstract class ComputerFamilyRecipe extends ComputerConvertRecipe {
         }
 
         @Override
-        public void toNetwork(@Nonnull FriendlyByteBuf buf, @Nonnull T recipe) {
+        public void toNetwork(FriendlyByteBuf buf, T recipe) {
             buf.writeVarInt(recipe.getWidth());
             buf.writeVarInt(recipe.getHeight());
             buf.writeUtf(recipe.getGroup());

src/main/java/dan200/computercraft/shared/computer/recipe/ComputerUpgradeRecipe.java

@@ -14,20 +14,16 @@ import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.crafting.Ingredient;
 import net.minecraft.world.item.crafting.RecipeSerializer;
 
-import javax.annotation.Nonnull;
-
 public final class ComputerUpgradeRecipe extends ComputerFamilyRecipe {
     private ComputerUpgradeRecipe(ResourceLocation identifier, String group, int width, int height, NonNullList<Ingredient> ingredients, ItemStack result, ComputerFamily family) {
         super(identifier, group, width, height, ingredients, result, family);
     }
 
-    @Nonnull
     @Override
-    protected ItemStack convert(@Nonnull IComputerItem item, @Nonnull ItemStack stack) {
+    protected ItemStack convert(IComputerItem item, ItemStack stack) {
         return item.withFamily(stack, getFamily());
     }
 
-    @Nonnull
     @Override
     public RecipeSerializer<?> getSerializer() {
         return ModRegistry.RecipeSerializers.COMPUTER_UPGRADE.get();

src/main/java/dan200/computercraft/shared/computer/terminal/TerminalState.java

@@ -37,7 +37,7 @@ public class TerminalState {
     @Nullable
     private final ByteBuf buffer;
 
-    private ByteBuf compressed;
+    private @Nullable ByteBuf compressed;
 
     public TerminalState(@Nullable NetworkedTerminal terminal) {
         this(terminal, true);

src/main/java/dan200/computercraft/shared/computer/upload/FileUpload.java

@@ -7,7 +7,6 @@ package dan200.computercraft.shared.computer.upload;
 
 import dan200.computercraft.ComputerCraft;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.nio.ByteBuffer;
 import java.security.MessageDigest;
@@ -29,12 +28,10 @@ public class FileUpload {
         this.checksum = checksum;
     }
 
-    @Nonnull
     public String getName() {
         return name;
     }
 
-    @Nonnull
     public ByteBuffer getBytes() {
         return bytes;
     }
@@ -43,7 +40,6 @@ public class FileUpload {
         return length;
     }
 
-    @Nonnull
     public byte[] getChecksum() {
         return checksum;
     }

src/main/java/dan200/computercraft/shared/data/BlockNamedEntityLootCondition.java

@@ -13,7 +13,6 @@ import net.minecraft.world.level.storage.loot.parameters.LootContextParams;
 import net.minecraft.world.level.storage.loot.predicates.LootItemCondition;
 import net.minecraft.world.level.storage.loot.predicates.LootItemConditionType;
 
-import javax.annotation.Nonnull;
 import java.util.Collections;
 import java.util.Set;
 
@@ -33,14 +32,12 @@ public final class BlockNamedEntityLootCondition implements LootItemCondition {
         return tile instanceof Nameable nameable && nameable.hasCustomName();
     }
 
-    @Nonnull
     @Override
     public Set<LootContextParam<?>> getReferencedContextParams() {
         return Collections.singleton(LootContextParams.BLOCK_ENTITY);
     }
 
     @Override
-    @Nonnull
     public LootItemConditionType getType() {
         return ModRegistry.LootItemConditionTypes.BLOCK_NAMED.get();
     }

src/main/java/dan200/computercraft/shared/data/ConstantLootConditionSerializer.java

@@ -12,8 +12,6 @@ import net.minecraft.world.level.storage.loot.Serializer;
 import net.minecraft.world.level.storage.loot.predicates.LootItemCondition;
 import net.minecraft.world.level.storage.loot.predicates.LootItemConditionType;
 
-import javax.annotation.Nonnull;
-
 public final class ConstantLootConditionSerializer<T extends LootItemCondition> implements Serializer<T> {
     private final T instance;
 
@@ -26,12 +24,11 @@ public final class ConstantLootConditionSerializer<T extends LootItemCondition>
     }
 
     @Override
-    public void serialize(@Nonnull JsonObject json, @Nonnull T object, @Nonnull JsonSerializationContext context) {
+    public void serialize(JsonObject json, T object, JsonSerializationContext context) {
     }
 
-    @Nonnull
     @Override
-    public T deserialize(@Nonnull JsonObject json, @Nonnull JsonDeserializationContext context) {
+    public T deserialize(JsonObject json, JsonDeserializationContext context) {
         return instance;
     }
 }

src/main/java/dan200/computercraft/shared/data/HasComputerIdLootCondition.java

@@ -13,7 +13,6 @@ import net.minecraft.world.level.storage.loot.parameters.LootContextParams;
 import net.minecraft.world.level.storage.loot.predicates.LootItemCondition;
 import net.minecraft.world.level.storage.loot.predicates.LootItemConditionType;
 
-import javax.annotation.Nonnull;
 import java.util.Collections;
 import java.util.Set;
 
@@ -33,14 +32,12 @@ public final class HasComputerIdLootCondition implements LootItemCondition {
         return tile instanceof IComputerTile computer && computer.getComputerID() >= 0;
     }
 
-    @Nonnull
     @Override
     public Set<LootContextParam<?>> getReferencedContextParams() {
         return Collections.singleton(LootContextParams.BLOCK_ENTITY);
     }
 
     @Override
-    @Nonnull
     public LootItemConditionType getType() {
         return ModRegistry.LootItemConditionTypes.HAS_ID.get();
     }

src/main/java/dan200/computercraft/shared/data/PlayerCreativeLootCondition.java

@@ -13,7 +13,6 @@ import net.minecraft.world.level.storage.loot.parameters.LootContextParams;
 import net.minecraft.world.level.storage.loot.predicates.LootItemCondition;
 import net.minecraft.world.level.storage.loot.predicates.LootItemConditionType;
 
-import javax.annotation.Nonnull;
 import java.util.Collections;
 import java.util.Set;
 
@@ -33,14 +32,12 @@ public final class PlayerCreativeLootCondition implements LootItemCondition {
         return entity instanceof Player player && player.getAbilities().instabuild;
     }
 
-    @Nonnull
     @Override
     public Set<LootContextParam<?>> getReferencedContextParams() {
         return Collections.singleton(LootContextParams.THIS_ENTITY);
     }
 
     @Override
-    @Nonnull
     public LootItemConditionType getType() {
         return ModRegistry.LootItemConditionTypes.PLAYER_CREATIVE.get();
     }

src/main/java/dan200/computercraft/shared/integration/jei/JEIComputerCraft.java

@@ -23,12 +23,10 @@ import mezz.jei.api.runtime.IJeiRuntime;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.item.ItemStack;
 
-import javax.annotation.Nonnull;
 import java.util.Collections;
 
 @JeiPlugin
 public class JEIComputerCraft implements IModPlugin {
-    @Nonnull
     @Override
     public ResourceLocation getPluginUid() {
         return new ResourceLocation(ComputerCraft.MOD_ID, "jei");

src/main/java/dan200/computercraft/shared/integration/jei/RecipeResolver.java

@@ -16,14 +16,12 @@ import mezz.jei.api.recipe.category.IRecipeCategory;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.crafting.CraftingRecipe;
 
-import javax.annotation.Nonnull;
 import java.util.Collections;
 import java.util.List;
 
 class RecipeResolver implements IRecipeManagerPlugin {
     private final UpgradeRecipeGenerator<CraftingRecipe> resolver = new UpgradeRecipeGenerator<>(x -> x);
 
-    @Nonnull
     @Override
     public <V> List<RecipeType<?>> getRecipeTypes(IFocus<V> focus) {
         var value = focus.getTypedValue().getIngredient();
@@ -41,9 +39,8 @@ class RecipeResolver implements IRecipeManagerPlugin {
         };
     }
 
-    @Nonnull
     @Override
-    public <T, V> List<T> getRecipes(@Nonnull IRecipeCategory<T> recipeCategory, IFocus<V> focus) {
+    public <T, V> List<T> getRecipes(IRecipeCategory<T> recipeCategory, IFocus<V> focus) {
         if (!(focus.getTypedValue().getIngredient() instanceof ItemStack stack) || recipeCategory.getRecipeType() != RecipeTypes.CRAFTING) {
             return Collections.emptyList();
         }
@@ -55,9 +52,8 @@ class RecipeResolver implements IRecipeManagerPlugin {
         };
     }
 
-    @Nonnull
     @Override
-    public <T> List<T> getRecipes(@Nonnull IRecipeCategory<T> recipeCategory) {
+    public <T> List<T> getRecipes(IRecipeCategory<T> recipeCategory) {
         return Collections.emptyList();
     }
 

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

@@ -24,7 +24,6 @@ import net.minecraft.world.item.TooltipFlag;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.level.LevelReader;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.List;
 
@@ -35,8 +34,7 @@ public class ItemDisk extends Item implements IMedia, IColouredItem {
         super(settings);
     }
 
-    @Nonnull
+    public static ItemStack createFromIDAndColour(int id, @Nullable String label, int colour) {
-    public static ItemStack createFromIDAndColour(int id, String label, int colour) {
         var stack = new ItemStack(ModRegistry.Items.DISK.get());
         setDiskID(stack, id);
         ModRegistry.Items.DISK.get().setLabel(stack, label);
@@ -45,7 +43,7 @@ public class ItemDisk extends Item implements IMedia, IColouredItem {
     }
 
     @Override
-    public void fillItemCategory(@Nonnull CreativeModeTab tabs, @Nonnull NonNullList<ItemStack> list) {
+    public void fillItemCategory(CreativeModeTab tabs, NonNullList<ItemStack> list) {
         if (!allowedIn(tabs)) return;
         for (var colour = 0; colour < 16; colour++) {
             list.add(createFromIDAndColour(-1, null, Colour.VALUES[colour].getHex()));
@@ -53,7 +51,7 @@ public class ItemDisk extends Item implements IMedia, IColouredItem {
     }
 
     @Override
-    public void appendHoverText(@Nonnull ItemStack stack, @Nullable Level world, @Nonnull List<Component> list, TooltipFlag options) {
+    public void appendHoverText(ItemStack stack, @Nullable Level world, List<Component> list, TooltipFlag options) {
         if (options.isAdvanced()) {
             var id = getDiskID(stack);
             if (id >= 0) {
@@ -69,12 +67,12 @@ public class ItemDisk extends Item implements IMedia, IColouredItem {
     }
 
     @Override
-    public String getLabel(@Nonnull ItemStack stack) {
+    public @Nullable String getLabel(ItemStack stack) {
         return stack.hasCustomHoverName() ? stack.getHoverName().getString() : null;
     }
 
     @Override
-    public boolean setLabel(@Nonnull ItemStack stack, String label) {
+    public boolean setLabel(ItemStack stack, @Nullable String label) {
         if (label != null) {
             stack.setHoverName(Component.literal(label));
         } else {
@@ -84,7 +82,7 @@ public class ItemDisk extends Item implements IMedia, IColouredItem {
     }
 
     @Override
-    public IMount createDataMount(@Nonnull ItemStack stack, @Nonnull Level world) {
+    public @Nullable IMount createDataMount(ItemStack stack, Level world) {
         var diskID = getDiskID(stack);
         if (diskID < 0) {
             diskID = ComputerCraftAPI.createUniqueNumberedSaveDir(world, "disk");
@@ -93,17 +91,17 @@ public class ItemDisk extends Item implements IMedia, IColouredItem {
         return ComputerCraftAPI.createSaveDirMount(world, "disk/" + diskID, ComputerCraft.floppySpaceLimit);
     }
 
-    public static int getDiskID(@Nonnull ItemStack stack) {
+    public static int getDiskID(ItemStack stack) {
         var nbt = stack.getTag();
         return nbt != null && nbt.contains(NBT_ID) ? nbt.getInt(NBT_ID) : -1;
     }
 
-    private static void setDiskID(@Nonnull ItemStack stack, int id) {
+    private static void setDiskID(ItemStack stack, int id) {
         if (id >= 0) stack.getOrCreateTag().putInt(NBT_ID, id);
     }
 
     @Override
-    public int getColour(@Nonnull ItemStack stack) {
+    public int getColour(ItemStack stack) {
         var colour = IColouredItem.getColourBasic(stack);
         return colour == -1 ? Colour.WHITE.getHex() : colour;
     }

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

@@ -18,7 +18,7 @@ import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.TooltipFlag;
 import net.minecraft.world.level.Level;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.List;
 
 public class ItemPrintout extends Item {
@@ -45,14 +45,13 @@ public class ItemPrintout extends Item {
     }
 
     @Override
-    public void appendHoverText(@Nonnull ItemStack stack, Level world, @Nonnull List<Component> list, @Nonnull TooltipFlag options) {
+    public void appendHoverText(ItemStack stack, @Nullable Level world, List<Component> list, TooltipFlag options) {
         var title = getTitle(stack);
         if (title != null && !title.isEmpty()) list.add(Component.literal(title));
     }
 
-    @Nonnull
     @Override
-    public InteractionResultHolder<ItemStack> use(Level world, @Nonnull Player player, @Nonnull InteractionHand hand) {
+    public InteractionResultHolder<ItemStack> use(Level world, Player player, InteractionHand hand) {
         if (!world.isClientSide) {
             new HeldItemContainerData(hand)
                 .open(player, new ContainerHeldItem.Factory(ModRegistry.Menus.PRINTOUT.get(), player.getItemInHand(hand), hand));
@@ -60,8 +59,7 @@ public class ItemPrintout extends Item {
         return new InteractionResultHolder<>(InteractionResult.SUCCESS, player.getItemInHand(hand));
     }
 
-    @Nonnull
+    private ItemStack createFromTitleAndText(@Nullable String title, @Nullable String[] text, @Nullable String[] colours) {
-    private ItemStack createFromTitleAndText(String title, String[] text, String[] colours) {
         var stack = new ItemStack(this);
 
         // Build NBT
@@ -84,18 +82,15 @@ public class ItemPrintout extends Item {
         return stack;
     }
 
-    @Nonnull
+    public static ItemStack createSingleFromTitleAndText(@Nullable String title, @Nullable String[] text, @Nullable String[] colours) {
-    public static ItemStack createSingleFromTitleAndText(String title, String[] text, String[] colours) {
         return ModRegistry.Items.PRINTED_PAGE.get().createFromTitleAndText(title, text, colours);
     }
 
-    @Nonnull
+    public static ItemStack createMultipleFromTitleAndText(@Nullable String title, @Nullable String[] text, @Nullable String[] colours) {
-    public static ItemStack createMultipleFromTitleAndText(String title, String[] text, String[] colours) {
         return ModRegistry.Items.PRINTED_PAGES.get().createFromTitleAndText(title, text, colours);
     }
 
-    @Nonnull
+    public static ItemStack createBookFromTitleAndText(@Nullable String title, @Nullable String[] text, @Nullable String[] colours) {
-    public static ItemStack createBookFromTitleAndText(String title, String[] text, String[] colours) {
         return ModRegistry.Items.PRINTED_BOOK.get().createFromTitleAndText(title, text, colours);
     }
 
@@ -103,25 +98,25 @@ public class ItemPrintout extends Item {
         return type;
     }
 
-    public static String getTitle(@Nonnull ItemStack stack) {
+    public static String getTitle(ItemStack stack) {
         var nbt = stack.getTag();
-        return nbt != null && nbt.contains(NBT_TITLE) ? nbt.getString(NBT_TITLE) : null;
+        return nbt != null && nbt.contains(NBT_TITLE) ? nbt.getString(NBT_TITLE) : "";
     }
 
-    public static int getPageCount(@Nonnull ItemStack stack) {
+    public static int getPageCount(ItemStack stack) {
         var nbt = stack.getTag();
         return nbt != null && nbt.contains(NBT_PAGES) ? nbt.getInt(NBT_PAGES) : 1;
     }
 
-    public static String[] getText(@Nonnull ItemStack stack) {
+    public static String[] getText(ItemStack stack) {
         return getLines(stack, NBT_LINE_TEXT);
     }
 
-    public static String[] getColours(@Nonnull ItemStack stack) {
+    public static String[] getColours(ItemStack stack) {
         return getLines(stack, NBT_LINE_COLOUR);
     }
 
-    private static String[] getLines(@Nonnull ItemStack stack, String prefix) {
+    private static String[] getLines(ItemStack stack, String prefix) {
         var nbt = stack.getTag();
         var numLines = getPageCount(stack) * LINES_PER_PAGE;
         var lines = new String[numLines];

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

@@ -22,7 +22,6 @@ import net.minecraft.world.item.TooltipFlag;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.level.LevelReader;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.io.IOException;
 import java.util.List;
@@ -37,27 +36,27 @@ public class ItemTreasureDisk extends Item implements IMedia {
     }
 
     @Override
-    public void fillItemCategory(@Nonnull CreativeModeTab group, @Nonnull NonNullList<ItemStack> stacks) {
+    public void fillItemCategory(CreativeModeTab group, NonNullList<ItemStack> stacks) {
     }
 
     @Override
-    public void appendHoverText(@Nonnull ItemStack stack, @Nullable Level world, @Nonnull List<Component> list, @Nonnull TooltipFlag tooltipOptions) {
+    public void appendHoverText(ItemStack stack, @Nullable Level world, List<Component> list, TooltipFlag tooltipOptions) {
         var label = getTitle(stack);
         if (!label.isEmpty()) list.add(Component.literal(label));
     }
 
     @Override
-    public boolean doesSneakBypassUse(@Nonnull ItemStack stack, LevelReader world, BlockPos pos, Player player) {
+    public boolean doesSneakBypassUse(ItemStack stack, LevelReader world, BlockPos pos, Player player) {
         return true;
     }
 
     @Override
-    public String getLabel(@Nonnull ItemStack stack) {
+    public String getLabel(ItemStack stack) {
         return getTitle(stack);
     }
 
     @Override
-    public IMount createDataMount(@Nonnull ItemStack stack, @Nonnull Level world) {
+    public @Nullable IMount createDataMount(ItemStack stack, Level world) {
         var rootTreasure = getTreasureMount();
         if (rootTreasure == null) return null;
 
@@ -93,23 +92,21 @@ public class ItemTreasureDisk extends Item implements IMedia {
         return result;
     }
 
-    private static IMount getTreasureMount() {
+    private static @Nullable IMount getTreasureMount() {
         return ComputerCraftAPI.createResourceMount("computercraft", "lua/treasure");
     }
 
-    @Nonnull
+    private static String getTitle(ItemStack stack) {
-    private static String getTitle(@Nonnull ItemStack stack) {
         var nbt = stack.getTag();
         return nbt != null && nbt.contains(NBT_TITLE) ? nbt.getString(NBT_TITLE) : "'missingno' by how did you get this anyway?";
     }
 
-    @Nonnull
+    private static String getSubPath(ItemStack stack) {
-    private static String getSubPath(@Nonnull ItemStack stack) {
         var nbt = stack.getTag();
         return nbt != null && nbt.contains(NBT_SUB_PATH) ? nbt.getString(NBT_SUB_PATH) : "dan200/alongtimeago";
     }
 
-    public static int getColour(@Nonnull ItemStack stack) {
+    public static int getColour(ItemStack stack) {
         var nbt = stack.getTag();
         return nbt != null && nbt.contains(NBT_COLOUR) ? nbt.getInt(NBT_COLOUR) : Colour.BLUE.getHex();
     }

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

@@ -11,7 +11,7 @@ import net.minecraft.sounds.SoundEvent;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.RecordItem;
 
-import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 /**
  * An implementation of IMedia for ItemRecords.
@@ -23,12 +23,12 @@ public final class RecordMedia implements IMedia {
     }
 
     @Override
-    public String getLabel(@Nonnull ItemStack stack) {
+    public @Nullable String getLabel(ItemStack stack) {
         return getAudioTitle(stack);
     }
 
     @Override
-    public String getAudioTitle(@Nonnull ItemStack stack) {
+    public @Nullable String getAudioTitle(ItemStack stack) {
         var item = stack.getItem();
         if (!(item instanceof RecordItem)) return null;
 
@@ -36,7 +36,7 @@ public final class RecordMedia implements IMedia {
     }
 
     @Override
-    public SoundEvent getAudio(@Nonnull ItemStack stack) {
+    public @Nullable SoundEvent getAudio(ItemStack stack) {
         var item = stack.getItem();
         if (!(item instanceof RecordItem)) return null;