获取异常:当我尝试在Spring jpa中执行左连接时为空；

@Entity
public class User {
    @Id
    private Long id;
    
    // ... 其他字段 ...

    @OneToMany(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private List<Order> orders;
    
    // ... getter 和 setter ...
}

String jpql = "SELECT u FROM User u LEFT JOIN FETCH u.orders WHERE u.id = :userId";
User user = entityManager.createQuery(jpql, User.class)
                           .setParameter("userId", userId)
                           .getSingleResult();

@Transactional
public User getUserWithOrders(Long userId) {
    String jpql = "SELECT u FROM User u LEFT JOIN FETCH u.orders WHERE u.id = :userId";
    return entityManager.createQuery(jpql, User.class)
                       .setParameter("userId", userId)
                       .getSingleResult();
}

@Entity
public class User {
    @Id
    private Long id;
    
    // ... 其他字段 ...

    @OneToMany(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private List<Order> orders;
    
    // ... getter 和 setter ...
}

@Entity
public class Order {
    @Id
    private Long id;
    
    // ... 其他字段 ...

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user;
    
    // ... getter 和 setter ...
}

@Transactional
public User getUserWithOrders(Long userId) {
    String jpql = "SELECT u FROM User u LEFT JOIN FETCH u.orders WHERE u.id = :userId";
    return entityManager.createQuery(jpql, User.class)
                       .setParameter("userId", userId)
                       .getSingleResult();
}