I'm wondering if there are implementations lying around about an IFUNKNOWN (or IFNULL) operator. The form would be Attribute.ifUnknown(defaultvalue). When the attribute Attribute has the value "null" the value of the expression defaultvalue (either a literal or the value of another attribute) will be returned. This operator should work for all types of attributes. This seems a very logical and handy operator. Has somebody already implemented this.