This is the companion issue of https://hibernate.atlassian.net/browse/HHH-12920 .

When running at DEBUG level, an exception can be thrown if you use the `AbstractCachedDomainDataAccess#clearCache()` method.

While the issue is not critical by itself, it can become a real issue if we want to debug something with a customer and we ask him to enable DEBUG: he will get an exception if this method is called.

Trivial patch is here: https://github.com/hibernate/hibernate-orm/pull/2500/files

msimka@redhat.com interested in your feedback on this one as it's not a real critical one. Thanks.