Native database connector:
If the object class has a virtual unique property as selection key property, which is a combination of several real columns, the above error message will be displayed if at least one of the columns is NULL. However, this is a restriction that is too intolerant.
This is a product defect (32817).
This will be fixed on a future release of the product. If you require this immediately corrected, please contact support for a hotfix referencing the defect ID 32817.