toJson method Null safety

Implementation

Map<String, Object?> toJson() {
  return {
    'screenToken': screenToken,
    'batteryPercentage': batteryPercentage,
    'lowBatteryThreshold': lowBatteryThreshold,
    'lowBatteryNotificationDelay': lowBatteryNotificationDelay,
    'batteryReportingDelay': batteryReportingDelay,
    'isOnline': isOnline,
  };
}