Don't return null when adding processors to NullExtent

(cherry picked from commit 1a8ad8133e)

worldedit-core/src/main/java/com/fastasyncworldedit/core/extent/NullExtent.java

@@ -219,16 +219,6 @@ public class NullExtent extends FaweRegionExtent implements IBatchProcessor {
         throw reason;
     }
 
-    @Override
-    public Extent addProcessor(final IBatchProcessor processor) {
-        return null;
-    }
-
-    @Override
-    public Extent addPostProcessor(final IBatchProcessor processor) {
-        return null;
-    }
-
     @Override
     public BlockArrayClipboard lazyCopy(Region region) {
         throw reason;