code: protected void onNewItems(@NonNull List<Model> newItems, int page) {
          OnNewItemsListener<Model> onNewItemsListener = this.mOnNewItemsListener;
          try {
              onNewItemsListener.onNewItems(newItems, page);
          } catch (NullPointerException npe) {
              // Lazy null checking! If this was our npe, then throw with an appropriate message.
              throw onNewItemsListener != null ? npe
                      : new NullPointerException("You must provide an `OnNewItemsListener`");
          }
      }
docs: The default implementation takes care of calling the previously set
  {@link OnNewItemsListener OnNewItemsListener}.
  
  @param newItems
  @param page
  @see #withOnNewItemsListener(OnNewItemsListener) withOnNewItemsListener(OnNewItemsListener)