toMap method Null safety

Implementation

@override
Map<String, Object?> toMap() {
  return Map.from(super.toMap())
    ..addAll({
      'items': this.items.map((coord) => coord.toMap()).toList(),
      'icon': this.icon,
      'pointSize': this.pointSize?.toMap(),
      'anchor': this.anchor?.toMap(),
    });
}