Some misunderstanding happened in the parent task.

Reporter wrote in description that exception happens in

org.hibernate.persister.entity.DiscriminatorType.nullSafeSet(PreparedStatement, Object, int, SessionImplementor)

method, but it called only when binding parameter to TYPE() expression.

I have the same issue when trying to write a query with optional parameters, e.g.:

SELECT p FROM Person p WHERE (:personType IS NULL OR TYPE(p) = :personType)

So the test case attached to the parent task is incorrect, see the attached modified test case to verify.

Exception happens because of this row in the org.hibernate.persister.entity.DiscriminatorType.nullSafeSet(PreparedStatement, Object, int, SessionImplementor) method:

String entityName = session.getFactory().getClassMetadata((Class) value).getEntityName();

When value is null getClassMetadata() throws NullPointerException.