MOQ REQUEST.Forms System.Argument Exception

Question

    public void SetupTests()
    {

        moqsession = new Mock<HttpSessionStateBase>(); 
        moqContext = new Mock<HttpContextBase>();
        moqRequest = new Mock<HttpRequestBase>();
        moqContext.Setup(x => x.Request).Returns(moqRequest.Object);
        moqContext.Setup(x => x.Session).Returns(moqsession.Object);
        // Create a "fake" form
        formValues = new NameValueCollection
{
    { "HiddenTransactionNumber", "0" }, 
    { "LastName", "Danylko" }                
};

    } 
    public void Test_withModel()
    {

        moqRequest.Setup(r => r.Form).Returns(formValues);

        var forms = moqContext.Object.Request.Form;
        // Assert
        Assert.IsNotNull(forms);

        ControllerContext ctx = new ControllerContext();
        ctx.HttpContext = moqContext.Object;

        var i = new Mock<IController>();
        i.Setup(d => d.FillViewBag());
        var A = new Model();
        A.Tno = Convert.ToInt64(0);
        var controller = new Controller(i.Object);
        controller.ControllerContext = ctx;
        controller.Index(A); 
    }

上面是moq Request.Forms的单元测试代码。但是，当我使用它获取运行时异常作为System.Argument。在Controller中，我的代码是myRequest.Form [“HTN”]