>In String you need to omit ?. String is not a simple type like integer, for example. So, you can pass null without declaring string?, just declare parameter as string.

So, the adjustment I made is this:

        ' Avoid to receive a null
        ' expC1 Value
        Public Function GetNonNullable(ByVal tcValue As String) As String
            Dim lcValue As Integer = ""

            ' If we have a value
            If Not tcValue Is DBNull.Value Then
                lcValue = tcValue
            End If

            Return lcValue
        End Function