toMap method Null safety

Implementation

@override
Map<String, Object?> toMap() {
  return {
    'relativeHumidity': this.relativeHumidity,
    'sensoryTemp': this.sensoryTemp,
    'phenomenon': this.phenomenon,
    'windDirection': this.windDirection,
    'updateTime': this.updateTime,
    'temperature': this.temperature,
    'windPower': this.windPower,
    'clouds': this.clouds,
    'hourlyPrecipitation': this.hourlyPrecipitation,
    'visibility': this.visibility,
    'O3': this.O3,
    'PM2_5': this.PM2_5,
    'NO2': this.NO2,
    'SO2': this.SO2,
    'airQualityIndex': this.airQualityIndex,
    'PM10': this.PM10,
    'CO': this.CO
  };
}