Dear all,
I just migrated from Hibernate v 3.5.4 to version 3.6.7. I made NO changes to the code (except for replacing the AnnotationConfiguration class with Configuration as per the relevant migration guide) nor to the mapping of my classes. But now my application crashes at startup with a NPE in the EntityJoinWalkerClass:

Exception in thread "main" java.lang.NullPointerException
at org.hibernate.loader.entity.EntityJoinWalker$AssociationInitCallbackImpl.locateKeyManyToOneTargetIndex(EntityJoinWalker.java:241)
at org.hibernate.loader.entity.EntityJoinWalker$AssociationInitCallbackImpl.findKeyManyToOneTargetIndices(EntityJoinWalker.java:222)
at org.hibernate.loader.entity.EntityJoinWalker$AssociationInitCallbackImpl.resolve(EntityJoinWalker.java:194)
at org.hibernate.loader.entity.EntityJoinWalker.<init>(EntityJoinWalker.java:76)
at org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:109)
at org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:71)
at org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:54)
at org.hibernate.loader.entity.BatchingEntityLoader.createBatchingEntityLoader(BatchingEntityLoader.java:133)
at org.hibernate.persister.entity.AbstractEntityPersister.createEntityLoader(AbstractEntityPersister.java:1914)
at org.hibernate.persister.entity.AbstractEntityPersister.createEntityLoader(AbstractEntityPersister.java:1937)
at org.hibernate.persister.entity.AbstractEntityPersister.createLoaders(AbstractEntityPersister.java:3205)
at org.hibernate.persister.entity.AbstractEntityPersister.postInstantiate(AbstractEntityPersister.java:3191)
at org.hibernate.persister.entity.SingleTableEntityPersister.postInstantiate(SingleTableEntityPersister.java:728)
at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:348)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1842)
at HibernateUtil.getSessionFactory(HibernateUtil.java:111)
at HibernateUtil.getSession(HibernateUtil.java:133)
at DbCleaner.dropTables(DbCleaner.java:54)
at DbCleaner.cleanAndResetDB(DbCleaner.java:40)
at DbCleaner.main(DbCleaner.java:168)

Unfortunately this kind of behavior is very difficult to debug, because Hibernate itself is very skimpy on details. Smells like something wrong with the mapping, but I wonder why it used to work fine and now it crashes with the new Hibernate release.

Any ideas what the problem could be or where I should be looking?

Thanks in advance
Emmanuele

I'm really new in the community (and in Hibernate also) so I may be infringing some rule while responding to a 2011 question or saying something incorrect.

I faced exactly the same problem. In my situation I had an elementcollection, eagerly loaded, in a class A with an Id association with another class B identified by a composite-id. The columns of B composite id were used in the joinColumns collection of A elementCollection attribute. When invoking buildSessionFactory, NPE was thrown.
After debugging the org.hibernate.loader.entity.EntityLoader.<init> code, I detected while reading a code comment, that the eagerly property was the problem (I still don't understand why) because the function of the NPE is only invoked if eager is used.

The code comment is "// for each association with a composite id containing key-many-to-one(s), find the bidirectional side of
// each key-many-to-one (if exists) to see if it is eager as well. If so, we need to track the indices", in file org.hibernate.loader.entity.EntityJoinWalker.

So to fix the problem, I removed the eager annotation of the elementCollection, and simulated it through accesing the attribute while the transaction is opened in the DAO.

EDIT: This happens to me in version 4.1.4-Final.