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public Employee findEmployeeByPostalCode(EntityManager entityManager, String postalCode) {
    CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    CriteriaQuery<Employee> criteriaQuery = criteriaBuilder.createQuery(Employee.class);
    
    Root<Address> addressRoot = criteriaQuery.from(Address.class);
    criteriaQuery.select(addressRoot.get("employee"));
    criteriaQuery.where(criteriaBuilder.equal(addressRoot.get("postalCode"), postalCode));
    
    TypedQuery<Employee> query = entityManager.createQuery(criteriaQuery);
    List<Employee> employees = query.getResultList();
    
    if (!employees.isEmpty()) {
        return employees.get(0);
    } else {
        return null;
    }
}