fix: Fix NullReferenceException in CodeGen (#2581)

* fix: Fix NullReferenceException in CodeGen

Credit to @andreyshade

* Changelog

Author: ShadauxCat

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -17,6 +17,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Fixed
 
+- Fixed: Fixed a null reference in codegen in some projects (#2581)
 - Fixed issue where the `OnClientDisconnected` client identifier was incorrect after a pending client connection was denied. (#2569)
 - Fixed warning "Runtime Network Prefabs was not empty at initialization time." being erroneously logged when no runtime network prefabs had been added (#2565)
 - Fixed issue where some temporary debug console logging was left in a merged PR. (#2562)

com.unity.netcode.gameobjects/Editor/CodeGen/CodeGenHelpers.cs

@@ -155,7 +155,7 @@ public static MethodReference MakeGeneric(this MethodReference self, params Type
         public static bool IsSubclassOf(this TypeReference typeReference, TypeReference baseClass)
         {
             var type = typeReference.Resolve();
-            if (type.BaseType == null || type.BaseType.Name == nameof(Object))
+            if (type?.BaseType == null || type.BaseType.Name == nameof(Object))
             {
                 return false;
             }