code: public boolean next() {
          checkState();
          if (mPlayerPlaylist.isEmpty()) {
              return false;
          }
          PlaybackService.play(getContext(), mClientKey, mPlayerPlaylist.next());
          return true;
      }
docs: Stop the current played track and load the next one if the playlist isn't empty.
  <p/>
  If the current played track is the last one, the first track will be loaded.
  
  @return false if current playlist is empty.