Fix issue introduced by 4123edd

lastValue may be null at this point, old is not

worldedit-core/src/main/java/com/sk89q/worldedit/internal/wna/WorldNativeAccess.java

@@ -84,7 +84,7 @@ default <B extends BlockStateHolder<B>> boolean setBlock(BlockVector3 position,
             if (sideEffects.getState(SideEffect.LIGHTING) == SideEffect.State.ON) {
                 updateLightingForBlock(pos);
             }
-            markAndNotifyBlock(pos, chunk, lastValue, newState, sideEffects);
+            markAndNotifyBlock(pos, chunk, old, newState, sideEffects);
         }
 
         return successful;