System.NullReferenceException

Function GetHtml(ByVal url As String, ByRef web As WebBrowser) As String
Dim WebString As String
Dim myURI As New Uri(url)
web.Url = myURI
WebString = web.Document.Body.InnerHtml
Return WebString
End Function

System.NullReferenceException!!!
AS Above !! How to solve it!! Thank!!

Which line?

Regardless of anything else, don't pass your WebBrowser ByRef. There's no reason to.

Thank, I found the problem is the "browser loading " Bcos the browser not d/l completed .
, the browser still blank and i used to get the innerhtml with blank document!! so got the error message!, !! thank!!