toJson method
Implementation
@override
Map<String, dynamic> toJson() => <String, dynamic>{
'id': id,
'title': title,
'performer': performer,
'audio_url': audioUrl,
'audio_duration': audioDuration,
'reply_markup': replyMarkup?.toJson(),
'input_message_content': inputMessageContent?.toJson(),
'@type': constructor,
};