The update of the Javassist dependency to 3.17.1 in 4.1.9 sometimes causes bridge methods to be proxied instead of the corresponding non-bridge methods.
The result is that that lazy-initialisation is not triggered when the non-bridge method is called directly leading to NullPointerException s.
As far as I can tell the relevant Javassist issue is JASSIST-162 . I'm not sure if there anything that can be done about this on the Hibernate side.

The attached test case sometimes fails inconsistently for me. Sometimes it seems to do the right thing.