'Alle alten (NULL)-Werte durch Nullstring ersetzen:
        Dim dv As New DataView
        Dim f As Boolean = False
        Dim c As Integer = 0
        dv.Table = DataGrid1.DataSource
 
        For i As Integer = 0 To dv.Table.Columns.Count - 1
            Dim drv As DataRowView
            For Each drv In dv
                If drv(i) Is System.DBNull.Value Then
                    drv(i) = ""
                    c += 1
                Else
                    'MsgBox(drv(i).ToString)
                End If
            Next
        Next
        MsgBox("Es wurden " & c & " Nullwerte gefunden und ersetzt!")