Pass a null value to an objectdatasource from dropdownlist default

Hi, I would like to pass a parameter to an objectdatasource from a dropdownlist.  The first Item of the dropdownlist reads "AllProducts" but when I pass it to the stored proc in the datasource i would actually like it to read null as the default.  How can I do this?

ddlProdSuite.DataSource = pscmd.ExecuteReader();
            ddlProdSuite.DataTextField = "PRODUCT";
            ddlProdSuite.DataValueField = "PRODUCT";
            ddlProdSuite.DataBind();
            psConn.Close();
            ddlProdSuite.Items.Insert(0, "AllProducts");        

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