A 'Missing Mandatory Sample Population' error is shown for a non-mandatory role.
1. Create a new ORM file.
2. Add the fact - Book(.Name) is reviewed by Person(.Name)
3. Add a uniquness constraint spanning both roles in the fact type.
4. Add a sample population entry to Book of 'War and Peace'
You will now see that a 'Missing Mandatory Sample Population' error is shown - 'Model Error: 'Book' instance 'War and Peace' in model 'ORMModel1' must participate in FactType 'BookIsReviewedByPerson'.'
Unless I am mistaken, this error should not show because the role is not mandatory.