toJson method Null safety

Implementation

@override
Map<String, dynamic> toJson() {
  final json = super.toJson();
  json['type'] = type;
  json.addAll({
    'name': name,
    'owner': owner?.toJson(),
    'static': isStatic,
    'const': isConst,
    'implicit': implicit,
    'abstract': isAbstract,
  });
  _setIfNotNull(json, 'location', location?.toJson());
  return json;
}