toJson method Null safety

Implementation

@override
Map<String, dynamic> toJson() {
  final json = <String, dynamic>{};
  json['type'] = type;
  json.addAll({
    'class': classRef?.toJson(),
    'accumulatedSize': accumulatedSize,
    'bytesCurrent': bytesCurrent,
    'instancesAccumulated': instancesAccumulated,
    'instancesCurrent': instancesCurrent,
  });
  return json;
}