实体：（省略了一些属性）
储存：

@Entity
@Table(name = "t_storage")
public class Storage implements Serializable {

    private static final long serialVersionUID = -8067092629525887737L;

    @Id
    @GeneratedValue
    private Long id;

    @Column
    private String name;

    @ManyToMany(fetch = FetchType.LAZY,cascade= CascadeType.REFRESH)
    @JoinTable(name = "t_purchase_storage", joinColumns = {@JoinColumn(name = "storage_id") },inverseJoinColumns = { @JoinColumn(name = "purchase_id") })
    private List<Purchase> purchases = Lists.newArrayList();

    @ManyToMany(fetch = FetchType.LAZY,cascade=CascadeType.ALL)
    @JoinTable(name = "auth_user_storage", joinColumns = {@JoinColumn(name = "storage_id")}, inverseJoinColumns =
            {@JoinColumn(name = "user_id")})
    private List<User> users = new ArrayList<>();
}

用户：

@Entity
@Table(name = "auth_user")
public class User implements Serializable {

    private static final long serialVersionUID = 2577286098148701829L;

    @Id
    @GeneratedValue
    private Long id;

    @ManyToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "auth_user_storage", joinColumns = {@JoinColumn(name = "user_id")}, inverseJoinColumns =
            {@JoinColumn(name = "storage_id")})
    private Set<Storage> storages = Sets.newHashSet();

    @Column(name = "username")
    private String username;
}

步骤：1.选择一些存储

List<Storage> storageList = storageService.findAllStorage(null);
        storageList.forEach(store -> {
            store.setPurchases(null);
            store.setCheckUsers(null);
            store.setUsers(null);
            store.setStorageBins(null);
        });
        return ResponseEntity.ok(JsonResult.success(storageList));

2.aoplog调用了userserviceimpl方法

controllerLog.setOperatorName(userService.findUserNameById(id));

此serviceimpl有@transaction

@Service
@Transactional
@Slf4j
public class UserServiceImpl implements UserService {

    @Override
    public String findUserNameById(Long userId) {
        return userRepository.findUsernameById(userId);
    }

}

执行userrepository.findusernamebyid时，setnull的上一个属性被删除
日志：

2021-03-29 17:04:06.991 [http-nio-7779-exec-1] INFO  com.~~.api.web.log.AopLog - 【返回值】：<200 OK,class   JsonResult {
    code: 001
    msg: ok
    data: [com.~~.entity.Storage@21]
},{}>

Hibernate: delete from t_checkuser_storage where storage_id=?  
Hibernate: delete from t_purchase_storage where storage_id=?  
Hibernate: delete from auth_user_storage where storage_id=?  
Hibernate: select username from auth_user where id=?

解决
删除serviceimpl上的事务注解，则没有问题。
或不设为空，返回vo。
问题
我没有做任何保存或删除操作。为什么要删除留空的属性？