SQL Storage: <> and NOT IN for multivalued properties

For multivalued properties, the semantics are a bit twisted.

For instance:
dc:subjects IN ('foo', 'bar)
is translated to:
EXISTS (SELECT 1 FROM dc_subjects WHERE dc_subjects.id = hierarchy.id AND dc_subjects.item IN ('foo', 'bar'))

But the inverse:
dc:subjects NOT IN ('foo', 'bar)
is translated to:
NOT EXISTS (SELECT 1 FROM dc_subjects WHERE dc_subjects.id = hierarchy.id AND dc_subjects.item IN ('foo', 'bar'))