The problem affects also version 5.0.5.

The error message is different: org.hibernate.QueryException: Unsupported discriminator type null

The column in SQL contains a class. Using a class name in hibernate leads to the error above when calling:
eg: criteria = session.createCriteria(Employee.class)
.add(Restrictions.eq(Employee.FIELD_CLASS_TYPE, Employee.class));

you can test it with the attached source files in src.rar. you just need to create a sql database dbhibernatehhh9008 as specified in the attached hibernate.cfg.xml file.
src.rar