code: protected void onLoadMore(@NonNull ResultReceiver<Model> out, int currentPage) {
          OnLoadMoreHandler<Model> loadMoreHandler = this.mOnLoadMoreHandler;
          try {
              loadMoreHandler.onLoadMore(out, currentPage);
          } catch (NullPointerException npe) {
              // Lazy null checking! If this was our npe, then throw with an appropriate message.
              throw loadMoreHandler != null ? npe
                      : new NullPointerException("You must provide an `OnLoadMoreHandler`");
          }
      }
docs: The default implementation takes care of calling the previously set
  {@link OnLoadMoreHandler OnLoadMoreHandler}.
  
  @param out
  @param currentPage
  @see #withOnLoadMoreHandler(OnLoadMoreHandler) withOnLoadMoreHandler(OnLoadMoreHandler)