我知道这是一个菜鸟问题，对不起。我正在尝试使用Hibernates session.merge（）方法编辑现有记录，但出现以下错误：

java.lang.IllegalArgumentException: id to load is required for loading

这是我的对象：

@Id
@GeneratedValue(strategy = IDENTITY)
@Column(name = "TITLE_ID", unique = true, nullable = false)
private Integer titleId;

@NotNull
@NotBlank
@Column(name = "TITLE_DESCRIPTION", nullable = false, length = 10)
private String titleDescription;
// default constructor, getters & setters

这是服务层方法：

 public void edit(Title title) {
     logger.debug("Editing existing title");

     // Retrieve session from Hibernate
     Session session = sessionFactory.getCurrentSession();

     // Retrieve existing title via id
     Title existingTitle = (Title) session.get(Title.class, title.getTitleId());

     // Assign updated values to this title
     existingTitle.setTitleDescription(title.getTitleDescription());

     // Save updates
     session.merge(existingTitle);
 }

这是控制器的POST方法：

@RequestMapping(value="/edit", method = RequestMethod.POST)
public String postEditTitle(@Valid @ModelAttribute("titleAttribute") Title title,
                        BindingResult result) {

    logger.debug("Received request to edit title");

    if (result.hasErrors()) {
        return "editTitle";
    }
    else {
        titleService.edit(title);
        return "redirect:/essays/main/title";
    }
}

我想念什么？任何帮助都感激不尽。