toJson method Null safety

Implementation

@override
Map<String, dynamic> toJson() {
  final json = <String, dynamic>{};
  json['type'] = type;
  json.addAll({
    'recorderName': recorderName,
    'availableStreams': availableStreams?.map((f) => f).toList(),
    'recordedStreams': recordedStreams?.map((f) => f).toList(),
  });
  return json;
}