class ChatUser { final int id; final String name; final String? avatar; const ChatUser({required this.id, required this.name, this.avatar}); factory ChatUser.fromJson(Map jsonMap) => ChatUser( id: jsonMap["id"], name: jsonMap["name"], avatar: jsonMap['avatar'], ); //this didn't work because default parameter value must be cosnt and factory cannot be const factory ChatUser.zero() => ChatUser(id: 0, name: ''); }