>It isn't really nulls - it's a nullable structure

Ok, thanks, BTW, I have this:

        ' Avoid to receive a null
        ' expD1 Value
        Public Function GetNonNullable(ByVal tdValue As Date?) As Date
            Dim ldValue As Date = Nothing

            ' If we have a value
            If tdValue.HasValue Then
                ldValue = tdValue
            Else
                ldValue = oApp.GetEmptyDate()
            End If

            Return ldValue
        End Function

        ' Avoid to receive a null
        ' expN1 Value
        Public Function GetNonNullable(ByVal tnValue As Double?) As Double
            Dim lnValue As Double = 0

            ' If we have a value
            If tnValue.HasValue Then
                lnValue = tnValue
            End If

            Return lnValue
        End Function

        ' Avoid to receive a null
        ' expL1 Value
        Public Function GetNonNullable(ByVal tlValue As Boolean?) As Boolean
            Dim llValue As Double = False

            ' If we have a value
            If tlValue.HasValue Then
                llValue = tlValue
            End If

            Return llValue
        End Function

        ' Avoid to receive a null
        ' expN1 Value
        Public Function GetNonNullable(ByVal tnValue As Integer?) As Integer
            Dim lnValue As Integer = 0

            ' If we have a value
            If tnValue.HasValue Then
                lnValue = tnValue
            End If

            Return lnValue
        End Function

        ' 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 tcValue.HasValue Then
                lcValue = tcValue
            End If

            Return lcValue
        End Function

However, for the String type, the designer gives an error. It says "Type 'String' must be a value type or a type argument constrained to 'Structure' in order to be used with 'Nullable' or nullable modifier '?'". I will try with the other approach to see if that would work.