toJson method Null safety

Implementation

Map<String, dynamic> toJson() {
  final Map<String, dynamic> data = <String, dynamic>{};
  if (large != null) {
    data['Large'] = large!.toJson();
  }
  if (mid != null) {
    data['Mid'] = mid!.toJson();
  }
  if (marathon != null) {
    data['Marathon'] = marathon!.toJson();
  }
  if (fast != null) {
    data['Fast'] = fast!.toJson();
  }
  return data;
}