toMap method Null safety

Implementation

@override
Map<String, Object?> toMap() {
  return {
    'code': this.code,
    'name': this.name,
    'center': this.center?.toMap(),
    'paths': this
        .paths
        ?.map((list) => list.map((coord) => coord.toMap()).toList())
        .toList()
  };
}