public function getOneSignalDeviceType(): ?string 	{ 		$device_types = [ 			self::DEVICE_TYPE_IOS => 'iOS', 			self::DEVICE_TYPE_ANDROID => 'Android', 			self::DEVICE_TYPE_AMAZON => 'Amazon', 			self::DEVICE_TYPE_WINDOWS_PHONE => 'Windows Phone', 			self::DEVICE_TYPE_CHROME_APP => 'Chrome App / Extension', 			self::DEVICE_TYPE_CHROME_WEB_PUSH => 'Chrome Web Push', 			self::DEVICE_TYPE_WINDOWS => 'Windows', 			self::DEVICE_TYPE_SAFARI => 'Safari', 			self::DEVICE_TYPE_FIREFOX => 'Firefox', 			self::DEVICE_TYPE_MACOS => 'MacOS', 			self::DEVICE_TYPE_ALEXA => 'Alexa', 			self::DEVICE_TYPE_EMAIL => 'E-mail', 			self::DEVICE_TYPE_HUAWEI => 'Huawei', 			self::DEVICE_TYPE_SMS => 'SMS', 		];  		return $device_types[$this->device_type] ?? null; 	}