note on `null`ed parts removed on `rebuild` call

README.md

@@ -53,7 +53,7 @@ brikz.rebuild();
 api.publishedBar(...);
 ```
 
-You can add / delete / change parts later and call `rebuild` again. Parts that are not functions, are left as is (their internal as well as API part); parts that are functions are instantiated again and merged in.
+You can add / delete / change parts later and call `rebuild` again. Parts that are not functions, are left as is (their internal as well as API part); parts that are functions are instantiated again and merged in. Parts that are `null`ed are removed.
 
 Advanced use
 ====