Test af StreamWriter før lukning

Jeg streamer data på til en webserver, men får flg. fejl "System.IO.IOException: Cannot close stream until all bytes are written"

Se eksempel.

Private Sub postThis(ByVal tekst As String)

    Dim encoding As ASCIIEncoding = New ASCIIEncoding
    Dim postData As String = tekst
    Dim data As Byte() = encoding.GetBytes(postData)

    'laver request.
    Dim myRequest As System.Net.HttpWebRequest = System.Net.WebRequest.Create("HTTP://XYZ.COM")
    myRequest.Method = "POST"
    myRequest.ContentType = "application/x-www-form-urlencoded"
    myRequest.ContentLength = data.Length

    Dim newStream As IO.StreamWriter = New IO.StreamWriter(myRequest.GetRequestStream)

    'Sender stream
    newStream.Write(tekst)
    newStream.Close()

End Sub

Hvordan tester man om newStream er tom, inden man lukker streameren?