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