anchor.diff:          return true;
         } else if (requestByUser) {
           //last element
  -        final curr = _current.value;
  +        final curr = _current.valueOrNull;
           if (curr != null) {
             _playlistAudioFinished.add(Playing(
               audio: curr.audio,
  
positive.code:           break;
          case METHOD_CURRENT:
            if (call.arguments == null) {
              final current = _current.value;
              if (current != null) {
                final finishedPlay = Playing(
                  audio: current.audio,
  
negative.code:   ///
    Future<void> seekBy(Duration by) async {
      // only if playing a song
      final playing = current.valueOrNull;
      if (playing != null) {
        final totalDuration = playing.audio.duration;
  
  