Spring data MongoDB无法在组聚合中映射\u id

我正在使用Spring数据MongoDB生成聚合查询。我曾经这样做过:

// 5. Rejoin the array with group.
group("email", "name", "surname", "birthday", "creationTime", "updateTime", "technology")
  .push(SCORES_FIELD).as(SCORES_FIELD));

生成的步骤(在日志中)如下:

"$group" : { 
    "_id" : { 
        "email" : "$_id",
        "name" : "$name" ,
        "surname" : "$surname" , 
        "birthday" : "$birthday" , 
        "creationTime" : "$creationTime" , 
        "updateTime" : "$updateTime" , 
        "technology" : "$technology"
    } ,
    "scores" : { "$push" : "$scores"}
}

这很好,我已经在Mongo shell上进行了测试,并给出了我想要的。

问题是,当我对Spring数据执行相同操作时,email字段(Mongo中的\u id字段)被映射为null。我的映射可能有问题,但我还没有弄清楚到底是什么。模型如下:

@Document(collection = "user")
public class User implements UserDetails {

    private static final long serialVersionUID = 1L;
    private String name;
    private String surname;
    private LocalDate birthday;

    @Id
    @Field("_id")
    private String email;
    private Collection<? extends GrantedAuthority> authorities;
    private String password;
    private Set<Score> scores;
    private LocalDateTime creationTime;
    private LocalDateTime updateTime;
    private String technology;

    // Getters and setters, hashmap, equals and toString

}

我做了其他的查询,一切都很顺利。我只有这个问题,这是我唯一做的聚合。