diff --git a/src/core/interfaces/gnss_block_interface.h b/src/core/interfaces/gnss_block_interface.h
index bb45902c1..dd7f1558e 100644
--- a/src/core/interfaces/gnss_block_interface.h
+++ b/src/core/interfaces/gnss_block_interface.h
@@ -52,29 +52,29 @@
 class GNSSBlockInterface
 {
 public:
-	virtual ~GNSSBlockInterface()
-	{}
-	virtual std::string role() = 0;
-	virtual std::string implementation() = 0;
-	virtual size_t item_size() = 0;
-	virtual void connect(gr::top_block_sptr top_block) = 0;
-	virtual void disconnect(gr::top_block_sptr top_block) = 0;
+    virtual ~GNSSBlockInterface()
+    {}
+    virtual std::string role() = 0;
+    virtual std::string implementation() = 0;
+    virtual size_t item_size() = 0;
+    virtual void connect(gr::top_block_sptr top_block) = 0;
+    virtual void disconnect(gr::top_block_sptr top_block) = 0;
 
-	virtual gr::basic_block_sptr get_left_block() = 0;
-	virtual gr::basic_block_sptr get_right_block() = 0;
+    virtual gr::basic_block_sptr get_left_block() = 0;
+    virtual gr::basic_block_sptr get_right_block() = 0;
 
-	virtual gr::basic_block_sptr get_left_block(int RF_channel)
-	{
-		assert(RF_channel >= 0);
-		if (RF_channel == 0){}; // avoid unused param warning
-		return NULL; // added to support raw array access (non pure virtual to allow left unimplemented)= 0;
-	}
-	virtual gr::basic_block_sptr get_right_block(int RF_channel)
-	{
-		assert(RF_channel >= 0);
-		if (RF_channel == 0){};  // avoid unused param warning
-		return NULL; // added to support raw array access (non pure virtual to allow left unimplemented)= 0;
-	}
+    virtual gr::basic_block_sptr get_left_block(int RF_channel)
+    {
+        assert(RF_channel >= 0);
+        if (RF_channel == 0){}; // avoid unused param warning
+        return nullptr; // added to support raw array access (non pure virtual to allow left unimplemented)= 0;
+    }
+    virtual gr::basic_block_sptr get_right_block(int RF_channel)
+    {
+        assert(RF_channel >= 0);
+        if (RF_channel == 0){};  // avoid unused param warning
+        return nullptr; // added to support raw array access (non pure virtual to allow left unimplemented)= 0;
+    }
 };
 
 #endif /*GNSS_SDR_GNSS_BLOCK_INTERFACE_H_*/