copyWith method 
    
    
    
  Implementation
  NewSongDataBMusic copyWith({
  int? volumeDelta,
  int? playTime,
  int? dfsId,
  int? bitrate,
  int? sr,
  String? name,
  int? id,
  int? size,
  String? extension,
}) {
  return NewSongDataBMusic()
    ..volumeDelta = volumeDelta ?? this.volumeDelta
    ..playTime = playTime ?? this.playTime
    ..dfsId = dfsId ?? this.dfsId
    ..bitrate = bitrate ?? this.bitrate
    ..sr = sr ?? this.sr
    ..name = name ?? this.name
    ..id = id ?? this.id
    ..size = size ?? this.size
    ..extension = extension ?? this.extension;
}