Web API ArgumentNullException was unhandled by user code

Question

I am trying to implement error handling in my WebAPI and I have ErrorController.cs with the following code:

public class ErrorController : ApiController
{
    [HttpGet, HttpPost, HttpPut, HttpDelete, HttpHead, HttpOptions, AcceptVerbs("PATCH")]
    public HttpResponseMessage Handle404()
    {
        var responseMessage = new HttpResponseMessage(HttpStatusCode.NotFound);
        responseMessage.ReasonPhrase = "The requested resource is not found";
        return Request.CreateResponse(new { error = "The requested resource is not found" });
    }
}

I make an API call like this:

http://localhost:46151/api/TData?ROOM=ABC&DOB_GT=01-SEP-05&DOB_LT=30-DEC-06&STATUS_TYPE=CMT

In order to force an error to occur I tried mispelling one of the query parameters (from DOB_LT to DO_LT) to check how errors are being handled -- like this:

http://localhost:46151/api/TData?ROOM=ABC&DOB_GT=01-SEP-05&DO_LT=30-DEC-06&STATUS_TYPE=CMT

The debugger breaks in ErrorController as shown in the image below:

Tried try Catch block like

        catch (Exception ex)
         {
             var returnObj = new { error = ex.Message };
             var response = Request.CreateResponse(HttpStatusCode.BadRequest, returnObj, MediaTypeHeaderValue.Parse("application/json"));
             ContentDispositionHeaderValue contentDisposition = null;
             if (ContentDispositionHeaderValue.TryParse("inline; filename=error.json", out contentDisposition))
             {
                 response.Content.Headers.ContentDisposition = contentDisposition;
             }
             return response;
         }