private async void saveReservation(Car car)
 {
     await DatabaseService.insertReservation(reservation, car, account.id).ContinueWith(task =>
     {
         bool result = task.Result;
         if (result)
         {
             MessageBox.Show("Zapisano");
             if (InvokeRequired)
             {
                 Invoke(new Action(() => Hide()));
             }
             else
             {
                 Hide();
             }
         }
         else
         {
             MessageBox.Show("Nie zapisano");
         }
     });
 }