Hql 查询map中key值？

public class StaffCourseTable extends BaseEntity {

@OneToMany(mappedBy = "courseTable")
@MapKey(name = "section")
private Map<Section, StaffCourseTableEntry> sectionEntries = new HashMap<Section, StaffCourseTableEntry>();

}

@SuppressWarnings("unchecked")
@Transactional(readOnly = true)
public List<Staff> findBySection(Section section) {
Query query = entityManager
.createQuery("select distinct table.staff from StaffCourseTable table  where (:section not in indices(table.sectionEntries) )");
query.setParameter("section", section);
return query.getResultList();
}