How to display invalid call exceptions from fluent controller in MVCContrib?

Question

How can I pass the exception thorwn by the action in MVCContrib.FluentController CheckValidCall(action)?

    [ExportModelStateToTempData]
    public ActionResult Index(int itemId, int page)
    {
        return CheckValidCall(() => MyService.GetResults(itemId, page))
            .Valid(x => View(x))
            .Invalid(() => RedirectToAction(RestfulAction.Index));
    } 

When GetResults() throws exception I want to display it in the view. I've tired ModelState

    <%if (ViewData.ModelState.ContainsKey("_FORM")) {%>
    <div class="notificationError">
        <%= ViewData.ModelState["_FORM"].Errors.FirstOrDefault().ErrorMessage %>            
    </div>
<%}%>

but the ModelState is valid and contains no errors. Is there any way to access the exception message without wrapping service method in try-catch block? If it helps here is my unit test to check ModelState which fails as TestController.ModelState.IsValid is true:

    [Fact]
    public void ServiceExceptionIsConvertedToModelStateErrorInFluentController()
    {
        // Set up
        MockService.Setup(x => x.GetResults(It.IsAny<int>(), It.IsAny<int>()))
            .Throws(new InvalidOperationException("Mocked Service Exception"));

        // Excercise
        Assert.Throws<InvalidOperationException>(() => TestController.GetResults(1, 1));

        // Verify
        Assert.False(TestController.ModelState.IsValid);
        Assert.True(TestController.ModelState["_FORM"].Errors.Count > 0);
    }

Answer 1

I've manage to pass exception into ModelState by overriding MvcContrib.FluentController.AbsteactFluentController.ExecuteCheckValidCall(Func action):

    protected override object ExecuteCheckValidCall(Func<object> action)
    {
        try
        {
            return base.ExecuteCheckValidCall(action);
        }
        catch (Exception exception)
        {
            ModelState.AddModelError("_Exception", exception);
            return null;
        }
    }

Which is called by CheckValidCall. However the method is described as "public for testing purposes only and shouldn't be used" the alternative way of doing it is to override MvcContrib.FluentController.AbstractFluentController.CheckValidCall().