private static bool CanSaveVehicle(Vehicle arg)
        {
            if (arg == null)
                return false;

            return !string.IsNullOrEmpty(arg.Make) && !string.IsNullOrEmpty(arg.Model);
        }
        private async Task SaveVehicle(Vehicle vehicle)
        {
            Working = true;

            await vehicle.Save();

            if(!Vehicles.Contains(vehicle))
                Vehicles.Add(vehicle);

            Working = false;
        }