toMap method Null safety

Implementation

@override
Map<String, Object?> toMap() {
  return {
    'imageNumber': this.imageNumber,
    'grouponNumber': this.grouponNumber,
    'checkInNumber': this.checkInNumber,
    'overallRating': this.overallRating,
    'favoriteNumber': this.favoriteNumber,
    'facilityRating': this.facilityRating,
    'tasteRating': this.tasteRating,
    'commentNumber': this.commentNumber,
    'discountNumber': this.discountNumber,
    'serviceRating': this.serviceRating,
    'tag': this.tag,
    'children': this.children?.map((v) => v.toMap()).toList(),
    'type': this.type,
    'hygieneRating': this.hygieneRating,
    'naviLocation': this.naviLocation?.toMap(),
    'distance': this.distance,
    'environmentRating': this.environmentRating,
    'technologyRating': this.technologyRating,
    'detailURL': this.detailURL,
    'price': this.price,
    'openingHours': this.openingHours,
  };
}