code: @SuppressWarnings("unchecked")
      protected E uniqueResult(Criteria criteria) throws HibernateException {
          return (E) requireNonNull(criteria).uniqueResult();
      }
docs: Convenience method to return a single instance that matches the criteria, or null if the
  criteria returns no results.
  
  @param criteria the {@link Criteria} query to run
  @return the single result or {@code null}
  @throws HibernateException if there is more than one matching result
  @see Criteria#uniqueResult()