toMap method Null safety

Implementation

@override
Map<String, Object?> toMap() {
  return {
    'totalPageNum': this.totalPageNum,
    'curPageIndex': this.curPageIndex,
    'totalPOINum': this.totalPOINum,
    'curPOINum': this.curPOINum,
    'poiInfoList': this.poiInfoList?.map((v) => v.toMap()).toList()
  };
}