@CreatedDate不起作用，但@UpdatedDate正在第一次保存

Question

我尝试使用@CreatedDate和@LastModifiedDate。虽然@LastModifiedDate可以正常工作，但@CreatedDate却不能。

我在主应用程序配置文件中添加了@EnableMongoAuditing。

mainapplication.java

public class Application {

    public static void main(String[] args) {

        ApplicationContext applicationContext = 
            SpringApplication.run(Application.class, args);

    }
}

Comment.java

@Entity
public class Comment {

    @Id
    String commentId;

    @NotNull
    String userId;

    @CreatedDate
    Date CreatedDate;

    @LastModifiedDate
    Date UpdatedDate;

    getters, setters .,,    
}

CommentDAO.java

public class CommentDAO{

    @Autowired
    MongoTemplate mongoTemplate;

    public Comment addComment(Comment comment) {

        return mongoTemplate.save(comment, "Comment");
    }
}

controller.java

 @annotations
 class controller
 {
    @GetMapping("/hello")
    public Comment check() 
    {
        Comment c=new Comment();
        c.setUserId("kli");
        c.setAnonymus(false);
        return commentDAO.addComment(c);
    }
 }

结果是

commentId   "0.07864261262777905"
userId  "kli"
content null
anonymus    false
createdDate null
updatedDate "2019-01-19T08:36:42.573+0000"