anchor.diff:  
   @immutable
   class Metas {
  +  final String id;
     final String title;
     final String artist;
     final String album;
  
positive.code:       if (metas.image.package != null)
          params["song.imagePackage"] = metas.image.package;
      }
    }
  }
  
  
negative.code:   final MetasImage image;
  
    const Metas({
      this.id,
      this.title,
      this.artist,
      this.album,
  