Get value of html select element on form post

I have a View that has a select drop-down list and an edit button within a form. What I want to do is have the user select one of the options from the select element, click on the edit button, and get the value of the selected option in the Controller method.
I created my form with <% Html.BeginForm(): %>
and the Controller "Edit" method should be called.
I looked through several online examples, but each one focused on how to set values and the default selected value of the select element, rather than retrieving it from the code in the Controller method. I tried grabbing it from the Request.Form collection like:
string val = Request.Form["myDropDownList"].ToString();
and also:
string val = Request.Form["myDropDownList"];
Obviously I didn't do this correctly, because I get a null reference exception. Does anyone have the solution to this issue?
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