We just found another problem related to this in one of our applications. The stacktrace is slightly different:

java.lang.NullPointerException
     at org.hibernate.type.descriptor.java.AbstractTypeDescriptor.extractHashCode(AbstractTypeDescriptor.java:88)
     at org.hibernate.type.AbstractStandardBasicType.getHashCode(AbstractStandardBasicType.java:210)
     at org.hibernate.type.AbstractStandardBasicType.getHashCode(AbstractStandardBasicType.java:214)
     at org.hibernate.engine.spi.CollectionKey.generateHashCode(CollectionKey.java:86)
     at org.hibernate.engine.spi.CollectionKey.<init>(CollectionKey.java:74)
     at org.hibernate.engine.spi.CollectionKey.<init>(CollectionKey.java:60)
     at org.hibernate.engine.loading.internal.CollectionLoadContext.getLoadingCollection(CollectionLoadContext.java:111)
     at org.hibernate.loader.Loader.handleEmptyCollections(Loader.java:1267)
     at org.hibernate.loader.Loader.doQuery(Loader.java:868)
     at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:293)
     at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:263)
     at org.hibernate.loader.Loader.loadCollectionBatch(Loader.java:2157)
     at org.hibernate.loader.collection.BatchingCollectionInitializer.initialize(BatchingCollectionInitializer.java:80)
     at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:678)
     at org.hibernate.event.internal.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:80)
     at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:1804)
     at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:549)
     at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:234)
     at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:545)
     at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:124)
     at org.hibernate.collection.internal.PersistentBag.toArray(PersistentBag.java:274)
     at java.util.Collections.sort(Collections.java:116)

One of my coworker is going to work on building a self contained test case for this case, too.

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