toMap method Null safety

Implementation

@override
Map<String, Object?> toMap() {
  return {
    'data': this
        .data
        .map((weightedCoordinate) => weightedCoordinate.toMap())
        .toList(),
    'radius': this.radius,
    'opacity': this.opacity,
    'gradient': this.gradient?.toMap()
  };
}