getConnectedPrinters method Null safety

Implementation

@override
Future<List<PrinterDevice>> getConnectedPrinters(
    {PrinterDeviceType? type}) async {
  List<PrinterDevice> list = List.empty(growable: true);
  switch (type) {
    case PrinterDeviceType.usb:
      var t = await _getConnectedUsbPrinters();
      if (t != null) {
        list.addAll(t);
      }
      break;
    case PrinterDeviceType.usbAccessory:
      var t = await _getConnectedUsbAccessoryPrinters();
      if (t != null) {
        list.addAll(t);
      }
      break;
    case PrinterDeviceType.tty:
      var t = await _getConnectedTtyPrinters();
      if (t != null) {
        list.addAll(t);
      }
      break;
    case PrinterDeviceType.tcp:
      var t = await _getConnectedTcpPrinters();
      if (t != null) {
        list.addAll(t);
      }
      break;
    case PrinterDeviceType.bluetooth:
      var t = await _getConnectedBluetoothPrinters();
      if (t != null) {
        list.addAll(t);
      }
      break;
    default:
      try {
        var t = await _getConnectedUsbPrinters();
        if (t != null) {
          list.addAll(t);
        }
      } catch (e) {}
      try {
        var t = await _getConnectedUsbAccessoryPrinters();
        if (t != null) {
          list.addAll(t);
        }
      } catch (e) {}
      try {
        var t = await _getConnectedTtyPrinters();
        if (t != null) {
          list.addAll(t);
        }
      } catch (e) {}
      try {
        var t = await _getConnectedTcpPrinters();
        if (t != null) {
          list.addAll(t);
        }
      } catch (e) {}
      try {
        var t = await _getConnectedBluetoothPrinters();
        if (t != null) {
          list.addAll(t);
        }
      } catch (e) {}
  }
  return Future.value(list);
}