I used to always asume that calling Session.load() would give me a proxy (or bytecode enhanced) object, but now I'm not sure if that's the case. It looks like now when I call load, I get an object with it's collections set to null, giving me null pointers when I try access them. What is the documented behavoir here?

There is not enough information, but I will take my best guess at what is happening. If your pojo doesn't initialize the collections in the default constructor, then they are null by default. If your collection is empty, hibernate will not set the collection, so it remains null. So, I would try initializing empty collections on object construction and see if that solves your problem.

Hmm, I guess I just assumed that Hibernate would give me an empty collections. Thanks!

Yes, Hibernate always returns empty collections, never nulls, when it instantates the object.

So am I right to assume that this should never be true?

session.load(o.class, id).getMappedCollection() == null

Because that's what's happening. I'm using the latest betas of Hibernate 3.1 and the annotations.