I'm getting the following exception when trying to persist a newly created entity using EJB3 RC5 in JBoss 4.0.3SP1 with jdk 1.5.0_06 running on Linux. After looking quickly at the code I don't see how GregorianCaleander can get in such a state, and I'm not proficient enough in Hibernate inner workings to understand what's the acctual cause.

Caused by: java.lang.NullPointerException
at java.util.GregorianCalendar.clone(GregorianCalendar.java:1864)
at org.hibernate.type.CalendarType.deepCopyNotNull(CalendarType.java:68)
at org.hibernate.type.MutableType.deepCopy(MutableType.java:25)
at org.hibernate.type.TypeFactory.deepCopy(TypeFactory.java:323)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:255)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:167)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:101)
at org.hibernate.event.def.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:131)
at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:87)
at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:38)
at org.hibernate.impl.SessionImpl.firePersist(SessionImpl.java:642)
at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:616)
at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:620)
at org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:127)
at org.jboss.ejb3.entity.InjectedEntityManager.persist(InjectedEntityManager.java:141)

Found the cause of this to be a bug in the current JDK, and for my case a session bean relation that was remote when it should be local. See http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6358365 for details.