bindingContext.ModelName is empty?

So I'm trying to apply Darin Dimitrov's answer, but in my implementation bindingContext.ModelName is equal to "".

Here's my viewmodel:

public class UrunViewModel
{
    public Urun Urun { get; set; }
    public Type UrunType { get; set; }
}

Here's the part of the view that posts the model types:

@model UrunViewModel

@{
    ViewBag.Title = "Tablo Ekle";

    var types = new List<Tuple<string, Type>>();
    types.Add(new Tuple<string, Type>("Tuval Baskı", typeof(TuvalBaski)));
    types.Add(new Tuple<string, Type>("Yağlı Boya", typeof(YagliBoya)));
}

<h2>Tablo Ekle</h2>

    @using (Html.BeginForm("UrunEkle", "Yonetici")) {
        @Html.ValidationSummary(true)
        <fieldset>
            <legend>Tablo</legend>

            @Html.DropDownListFor(m => m.UrunType, new SelectList(types, "Item2", "Item1" ))

And here's my custom model binder:

public class UrunBinder : DefaultModelBinder
{
    protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type type)
    {
        var typeValue = bindingContext.ValueProvider.GetValue(bindingContext.ModelName + ".Urun");

        var model = Activator.CreateInstance((Type)typeValue.ConvertTo(typeof(Type)));
            bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, type);

        return model;
    } 
}

Finally, the line in Global.asax.cs:

ModelBinders.Binders.Add(typeof(UrunViewModel), new UrunBinder());

Here inside the overridden CreateModel function, in debugging mode I can see that bindingContext.ModelName is equal to "". And also, typeValue is null so CreateInstance function fails.