Sync await NULL reference exception while populating selectlistitem in Razor View

Question

I am injecting my service in view to populate dropdown in razor like this

@inject Web.Services.MyService  Options

Now I am trying to populate my dropdown like this

<select asp-for="CityID" asp-items="await Options.GetCities();" class="form-control form-control-sm">
            <option>--Select--</option>
</select>

Getcities method is below

public async Task<IEnumerable<SelectListItem>> GetCities()

        {   

            var cities = await _cityrepository.ListAllAsync();

            var items = new List<SelectListItem>
            {
                new SelectListItem() { Value = null, Text = "All", Selected = true }
            };
            foreach (SetupCities city in cities)
            {
                items.Add(new SelectListItem() { Value = city.CityId.ToString(), Text = city.Name});
            }

            return items;
        }

I am getting following error

NullReferenceException: Object reference not set to an instance of an object.
EvolvedX.Web.Services.VMWHService.GetCities() in VMWHService.cs
+
            var cities = await _cityrepository.ListAllAsync();
AspNetCore.Views_Warehouse_CreateWarehouse.ExecuteAsync() in CreateWarehouse.cshtml
+
        <select asp-for="CityID" asp-items="await Options.GetCities();" class="form-control form-control-sm">

I can see as the first await hit getcities the function exit. what is the proper way to handle such scenario M function is exiting before completing the method when it found await that is causing my selectlistitem to be null. I want to know how i modify my code so that selectlistitem get filled null exception will be solved