Tenho a seguinte consulta do construtor de critérios

    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<Object> critQuery = cb.createQuery();

    Root<Role> role = critQuery.from(Role.class);

    //create a join between role and permission
    MapJoin<Role,String,Permission> perm = role.joinMap("permissions");
    critQuery.multiselect(role.get("label"), perm.key(), perm.value());

    //this line throws NPE
    Query query = em.createQuery(critQuery);

A última linha lança uma exceção de ponteiro nul

java.lang.NullPointerException
at org.hibernate.ejb.criteria.path.AbstractPathImpl.prepareAlias(AbstractPathImpl.java:246)
at org.hibernate.ejb.criteria.path.AbstractPathImpl.render(AbstractPathImpl.java:253)
at org.hibernate.ejb.criteria.path.AbstractPathImpl.renderProjection(AbstractPathImpl.java:261)