Setup Mocked ViewModel for Unit Testing

Here is the scenario:

I'm writing a test for my controller and need to setup a view model titled CheckoutViewModel. My controller method, Products does not take CheckoutViewModel as a parameter, so I cannot pass it in that way.

Currently, the test fails returning a Null Exception because CheckoutViewModel is not getting set and called.

Question: How can I setup my CheckoutViewModel with data.

Error Details:

• System.NullReferenceException

• Object reference not set to an instance of an object

Current Test

[TestMethod]
public void Products_ProductControllerIsCalled_ReturnsViewWithProducts()
{
    // Arrange
    var currentSession = _autoMoqer.GetMock<ICurrentSession>().Object;
    ProductController productController = new ProductController(currentSession);

    var checkoutViewModel = new CheckoutViewModel
    {
        CheckoutId = new Guid()
    };

    // Act
    ActionResult result = productController.Products();

    // Assert
    Assert.IsInstanceOfType(result, typeof(ViewResult));
}

Controller

 [AccectReadVerbs]
 public ActionResult Products()
 {
    CheckoutViewModel checkoutViewModel = GetCheckoutViewModel();
    var checkoutId = checkoutViewModel.CheckoutId;
    var result = _productOrchestrator.Products(checkoutId, currentSession)

    return View(result);
 }

Failing on this method

private CheckoutViewModel GetCheckoutViewModel()
{
    if(Session["CheckoutViewModel"] == null)
    {
        return new CheckoutViewModel();
    }
    return (CheckoutViewModel)Session["CheckoutViewModel"];
}