Java 使用spring数据更新@DBref

所以我们有一个带有@DBRef list的集合

/**
 * List of company users
 */
@DBRef
public List<CompanyUser> companyUsers = new ArrayList<>();

我知道@DBRef是个坏主意，但这不是我的主意，我也不是来投反对票的D

public Company addUserToCompany(String id, CompanyUser companyUser) throws CimplyfiveException{
    Query query = new Query(new Criteria("_id").is(new ObjectId(id)));
    Update update = new Update().addToSet("companyUsers", companyUser);
    return modify(query, update, Company.class);
}
public <T> T modify(final Query query, final Update update, final Class<T> clazz){
        return geMongoTemplate().findAndModify(query, update, clazz);
}

Cannot create a reference to an object with a NULL id.