Null exception in commerce controller

I am trying to create controller fro commerce as explained in the link below. However, I am getting NULL exception in the parameter of action. e.g. 

currentContent is null in

public class AlloyCategoryController : ContentControllerBase<AlloyNode>
{    public ActionResult Index(AlloyNode currentContent)    {        var model = PageViewModel.Create<AlloyNode>(currentContent);        return View(model);    }
}

https://world.episerver.com/blogs/sorby/dates/2017/9/add-commerce-to-an-alloy-web-site/