MVC app cancel button navigation

I have an MVC form which a user can arrive at from two entirely different controllers/views - I have a cancel button on the form that I would like to simply navigate the user back to their previous page, whichever one they came from.

The button is a straight HTML anchor, not an actionlink:

<a class="btn btn-primary cancelNav" href="">Cancel</a>

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On the client-side, I am using unobtrusive jQuery to attach an anonymous function to the link:

    $(document).on('click', '.cancelNav', function () {
        window.location.assign(document.referrer);
    });

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I have experimented with numerous approaches here, using window.location, window.history and have verified that the correct URL with params is being passed, but all result in:
"System.ArgumentException: The parameters dictionary contains a null entry for parameter 'id' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult Edit(Int32)'"
yet I can click the browser's back button with no issue.

Can someone tell me why?