Send a parameter (cannot be null) to the controller from the javascript of the view

See more:

ASP.NET

Java

MVC4

The following function GetProject is called on change of the dropdown in the view.

Javascript

<script>
    function GetProject(projId) {
        
        var selectedText = projId.options[projId.selectedIndex].innerHTML;

        var selectedValue = projId.value;
        
        var url = '@Url.Action("OpenEndedDetails", "ResponseController", new { @projId = "projId" }, null);
        url = url.replace('projId', encodeURIComponent(selectedValue));

        alert(url);
        window.location.href = url;
    }

</script>

ResponseController

public ActionResult OpenEndedDetails(int projId)
        {
            
            ResponseContext feedback = new ResponseContext();
           
            /* Conditions:
             * @All openended questions in a project
             * */
            List<Response> feedbacks = feedback.Responses.Where(resp => resp.Answer.Equals("0") && resp.ProjectID == projId).ToList();

            return View(feedbacks);
        }

Error:
The parameters dictionary contains a null entry for parameter 'projId' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult OpenEndedDetails(Int32)' in 'SmartAdminMvc.Controllers.ResponseController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter.
Parameter name: parameters


ProjId is a primary key of type int. I don't know how to get rid of this exception. I want the Url.Action to load my entire view, with the value that i pass from the dropdown.
I might have made some major blunders with code. Kindly correct it.
Please help me as i am stuck with this issue for long.
Thanks