当表单字段为空时，ModelAttribute不起作用

Question

单击登录按钮而不输入用户名或密码时，我收到以下消息 HTTP状态400 - 客户端发送的请求在语法上不正确（）。

这意味着它不会进入控制器。

    @Controller
    public class UserController {
    @RequestMapping(value = {"login"}, method = RequestMethod.GET)
    public String goLogin(Model model) {
        model.addAttribute("user", new User());
        return "login";
    }

    @RequestMapping(value = {"login"}, method = {RequestMethod.POST})
    public String doLogin(@ModelAttribute("user") User user,
                          Model model,
                          BindingResult bresult) {...}
    }

@Entity
@DynamicUpdate
@DynamicInsert
@Table(name = "user")
public class User {

    @Id
    @GeneratedValue
    @Column(name = "user_id")
    private int userId = 0;

    @Column(name = "user_login")
    private String userLogin = "";

    @Column(name = "user_pass")
    private String userPass = "";

    /*setter and getter methods*/

}

    <form:form action="login" commandName="user" method="post">
    User Name:<form:input path="userLogin" id="userLogin"/><br/>
    Password:<form:password path="userPass" id="userPass"/><br/>
    <input value="Login" type="submit">
    </form:form>