问JPA/Hibernate静态元模型属性未填充-NullPointerException？

...
Root<JPAAlbum> albm = cq.from(JPAAlbum.class);
... albm.get(JPAAlbum_.theme) ... ;

public static volatile SingularAttribute<JPAAlbum, JPATheme> theme;

    CriteriaBuilder cb = em.getCriteriaBuilder();

    CriteriaQuery<JPAAlbum> cq = cb.createQuery(JPAAlbum.class) ;
    Root<JPAAlbum> albm = cq.from(JPAAlbum.class);
    cq.where(cb.equal(albm.get(JPAAlbum_.theme).get(JPATheme_.id),
                        session.getTheme().getId())) ;

Caused by: java.lang.NullPointerException
    at org.hibernate.ejb.criteria.path.AbstractPathImpl.get(AbstractPathImpl.java:138)
    at net.wazari.dao.jpa.WebAlbumsDAOBean.getRestrictionToAlbumsAllowed(WebAlbumsDAOBean.java:55)

     for (ManagedType o : em.getMetamodel().getManagedTypes()) {
            log.warn("___") ;
            for (Object p : o.getAttributes()) {
                log.warn(((Attribute)p).getName()) ;
            }
        }

   log.warn("_+_"+JPAPhoto_.id+"_+_") ;

java.lang.NullPointerException
    at org.hibernate.ejb.criteria.path.AbstractPathImpl.get(AbstractPathImpl.java:138)
    at net.wazari.dao.test.TestMetaModel.foo(TestMetaModel.java:55)

ant compile
or
ant dist

 CLASSPATH=`sh runTest.sh` java org.junit.runner.JUnitCore  net.wazari.dao.test.TestMetaModel