code: public PostUpdate<Entity<T>> getOrCreatePostUpdate()
     {
        Node node = childNode.getOrCreate("post-update");
        PostUpdate<Entity<T>> postUpdate = new PostUpdateImpl<Entity<T>>(this, "post-update", childNode, node);
        return postUpdate;
     }
docs: If not already created, a new <code>post-update</code> element with the given value will be created.
  Otherwise, the existing <code>post-update</code> element will be returned.
  @return  a new or existing instance of <code>PostUpdate<Entity<T>></code>