=== H2 ===
EntityAgent.update(stale book)      -> org.hibernate.HibernateException: The database returned no natively generated values : com.ankurm.agent.Book
EntityManager.merge(stale book)     -> jakarta.persistence.OptimisticLockException
EntityAgent.update(row not in db)   -> org.hibernate.HibernateException: The database returned no natively generated values : com.ankurm.agent.Book
EntityAgent.upsert(new versioned)   -> org.hibernate.HibernateException: The database returned no natively generated values : com.ankurm.agent.Book

=== HSQLDB ===
EntityAgent.update(stale book)      -> jakarta.persistence.OptimisticLockException
EntityManager.merge(stale book)     -> jakarta.persistence.OptimisticLockException
EntityAgent.update(row not in db)   -> jakarta.persistence.OptimisticLockException
EntityAgent.upsert(new versioned)   -> jakarta.persistence.OptimisticLockException