toJson method Null safety

Implementation

@override
Map<String, dynamic> toJson() {
  final json = <String, dynamic>{};
  json['type'] = type;
  json.addAll({
    'id': id,
    'number': number,
    'name': name,
    'isSystemIsolateGroup': isSystemIsolateGroup,
    'isolates': isolates?.map((f) => f.toJson()).toList(),
  });
  return json;
}