jqGrid custom search filters - Null being allowed

Hello!

I was hoping if someone can help me understand how to have one or multiple parameters to be null and still execute the search with whatever filter options is chosen.

At the moment I have TWO dropdowns:

   url: "/DataService/Webservice2.asmx/filter?d=" + d+ "&n=" + n,

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lets say both parameters are filled, it executes with no issues. But when one is blank it will shoot me an error telling me:

Conversion from string "" to type 'Integer' is not valid.

^ that error is shown in the webservice:

        Dim n As Integer = HttpContext.Current.Request.QueryString("n")

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or

        Dim d As String = HttpContext.Current.Request.QueryString("d")

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depends on which one is left blank.


Thank you!