I've tested the OP repository with the example use case and I think this is an edge case that should work, but it doesn't.

What I think is happening is that Hibernate does not accept unbound generic type in fields on a class annotated with @Entity, maybe because it assumes to not be able to determine the relation type.

But in this particular case, the OP has an abstract class with InheritanceType.SINGLE_TABLE which has a field that references a subclass of itself, which then can only generate a foreign key referencing the very same table.