>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 ValuePublicFunction GetNonNullable(ByVal tcValue AsString) AsStringDim lcValue AsInteger = ""
' If we have a valueIfNot tcValue IsDBNull.Value Then
lcValue = tcValue
EndIfReturn lcValue
EndFunction