I'll explain what is happening for documentaiton purposes. Since eager fetching is activated it tries to pre-render the SQL for the entities during boot time. Before the fix, a random Type (i.e. one of the attribute types from one of the subtypes) is registered for attributes like relation or attributes on BaseEntity. This means that, when loading BaseEntity via entityManager.find(BaseEntity.class, 123) it would be random, which one of the relations is loaded. With the fix, we register null to signal that the attribute has to be handled specially. Apparently, I missed to handle this properly for this kind of usage. I only handled the usage in queries.