toJson method Null safety

Implementation

@override
Map<String, dynamic> toJson() {
  final json = <String, dynamic>{};
  json['type'] = type;
  json.addAll({
    'members': members?.map((f) => f.toJson()).toList(),
    'memoryUsage': memoryUsage?.toJson(),
  });
  _setIfNotNull(json, 'dateLastAccumulatorReset', dateLastAccumulatorReset);
  _setIfNotNull(json, 'dateLastServiceGC', dateLastServiceGC);
  return json;
}