In ABL, a temp-table field can be specified with an Unknown value (?), similar to null in Java. If you need to determine if a field has been set to the Unknown value (?), you can use one of the ProDataObject isSet() methods to test property by name or index. These methods return true if the corresponding temp-table field is set to a value other than the Unknown value (?) and return false if the field is set to the Unknown value (?). For more information on the isSet() methods, see ProDataObject class. If you want to set a column property so the corresponding temp-table field is set to the Unknown value (?), do not set the property to any value.