Combo Box for Blazor - How to implement the scenario with cascading combo boxes and validation

Currently, I'm trying to make your example https://demos.devexpress.com/blazor/ComboBox#CascadingLists work with an async SelectedItemChanged handler, since I need to do async database read operations in that handler.
I.e.

C#
<DxComboBox Data="@Countries"  
            TextFieldName="CountryName"  
            SelectedItem="@CurrentCountry"  
            SelectedItemChanged="@SelectedCountryChanged">  
</DxComboBox>  

@code {  
    List<Country> Countries = ...;  
    Country CurrentCountry;  

    async Task SelectedCountryChanged(Country country)  
    {  
        ...  
    }  
}  

This does not compile due to the async.
What does compile is this:

C#
<DxComboBox Data="@Countries"  
            TextFieldName="CountryName"  
            SelectedItem="@CurrentCountry"  
            SelectedItemChanged="@(async e => await SelectedCountryChanged(e))">  
</DxComboBox>  

@code {  
    List<Country> Countries = ...;  
    Country CurrentCountry;  

    async Task SelectedCountryChanged(Country country)  
    {  
        ...  
    }  
}  

But unfortunately, during runtime, I get this exception:

C#
System.ArgumentNullException: Value cannot be null. (Parameter 'accessor')  
   at Microsoft.AspNetCore.Components.Forms.FieldIdentifier.Create[TField](Expression`1 accessor)  
   at DevExpress.Blazor.Internal.DxEditorBase`2.CreateFieldIdentifier()  
   at DevExpress.Blazor.Internal.DxEditorBase`2.get_EditFormFieldIdentifier()  
   at DevExpress.Blazor.Internal.DxEditorBase`2.get_EditFormFieldClass()  
   at DevExpress.Blazor.DxComboBox`1.<BuildRenderTree>b__0_0(RenderTreeBuilder __builder2)  
   at Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.AddContent(Int32 sequence, RenderFragment fragment)  
   at Microsoft.AspNetCore.Components.CascadingValue`1.Render(RenderTreeBuilder builder)  
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment)  
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry)  
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()  
--- End of stack trace from previous location where exception was thrown ---  
   at Microsoft.AspNetCore.Components.Rendering.HtmlRenderer.HandleException(Exception exception)  
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()  
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessPendingRender()  
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.AddToRenderQueue(Int32 componentId, RenderFragment renderFragment)  
   at Microsoft.AspNetCore.Components.ComponentBase.StateHasChanged()  
   at Microsoft.AspNetCore.Components.ComponentBase.CallOnParametersSetAsync()  
   at Microsoft.AspNetCore.Components.ComponentBase.RunInitAndSetParametersAsync()  
   at Microsoft.AspNetCore.Components.Rendering.HtmlRenderer.HandleException(Exception exception)  
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.AddToPendingTasks(Task task)  
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.SetDirectParameters(ParameterView parameters)  
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderRootComponentAsync(Int32 componentId, ParameterView initialParameters)  
   at Microsoft.AspNetCore.Components.Rendering.HtmlRenderer.CreateInitialRenderAsync(Type componentType, ParameterView initialParameters)  
   at Microsoft.AspNetCore.Components.Rendering.HtmlRenderer.RenderComponentAsync(Type componentType, ParameterView initialParameters)  
   at Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContext.<>c__11`1.<<InvokeAsync>b__11_0>d.MoveNext()  
--- End of stack trace from previous location where exception was thrown ---  
   at Microsoft.AspNetCore.Mvc.ViewFeatures.RazorComponents.StaticComponentRenderer.PrerenderComponentAsync(ParameterView parameters, HttpContext httpContext, Type componentType)  
   at Microsoft.AspNetCore.Mvc.Rendering.HtmlHelperComponentExtensions.PrerenderedServerComponentAsync(HttpContext context, ServerComponentInvocationSequence invocationId, Type type, ParameterView parametersCollection)  
   at Microsoft.AspNetCore.Mvc.Rendering.HtmlHelperComponentExtensions.RenderComponentAsync[TComponent](IHtmlHelper htmlHelper, RenderMode renderMode, Object parameters)  
   at ZetaHelpdesk.MainBlazor.Pages.Pages__Host.<ExecuteAsync>b__10_1() in C:\p\ZetaHelpdesk\Source\Core\MainBlazor\Pages\_Host.cshtml:line 19  
   at Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperExecutionContext.SetOutputContentAsync()  
   at ZetaHelpdesk.MainBlazor.Pages.Pages__Host.ExecuteAsync()  
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync(IRazorPage page, ViewContext context)  
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync(IRazorPage page, ViewContext context, Boolean invokeViewStarts)  
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync(ViewContext context)  
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)  
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|29_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)  
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)  
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)  
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()  
--- End of stack trace from previous location where exception was thrown ---  
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)  
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)  
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)  
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync()  
--- End of stack trace from previous location where exception was thrown ---  
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)  
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)  
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)  
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)  
   at Microsoft.AspNetCore.Localization.RequestLocalizationMiddleware.Invoke(HttpContext context)  
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)  

My question:
How can I use an async SelectedItemChanged handler in DXComboBox?