Programmatically using a Query String Parameter

I have a SqlDataSource that may or may not have a QueryStringParameter present (depending on where the request is coming from).
 I am trying to use the following statement but get the error” Object reference not set to an instance of an object”.  After using the debugger, I know “QueryPictureID” has a value so I am guessing I have not set the ‘type’ correctly.
 Any help would be appreciated.
Thanks
John
Note: The 'lblQueryString.text' is just to help me debug.
Protected Sub SqlDataSource_GetNews_Selecting(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.SqlDataSourceSelectingEventArgs) Handles SqlDataSource_GetNews.Selecting If Request.Params("PictureID") Is Nothing Then lblQueryString.Text = "Query string not Present" Else Dim QueryPictureID As String QueryPictureID = Request.Params("Pictur ...