Test an INPUT-OUTPUT or OUTPUT parameter for the Unknown value (?)

For OUTPUT and INPUT-OUTPUT parameters, you can find out whether an output Unknown value (?) is returned by testing if the IsNull property is true or the Value property on the holder object equals null.

For example, in C#, to test the value of a holder object (Holder), check the isNULL or Value property, as shown:

if (Holder.isNull) | if (Holder.Value == null)