为什么我的嵌套POJO从运行中的表单返回null!1.x

在游戏中!framework1.5.1,为什么我的thingy.Owner返回空值?自动绑定不应该解决这个问题吗?

用户类

    package models;

@Entity
@Table(name="objtest_user")
public class User extends Model
{
    @Required
    public String username;

    @Password
    @Required
    public String password;

    public String fullname;

    public User(String username, String password, String fullname)
    {
        this.username = username;
        this.password = password;
        this.fullname = fullname;
    }

    @Override
    public String toString()
    {
        return this.fullname;
    }
}

还有这个引用用户类的Thingy类

    package models;

import java.util.*;
import javax.persistence.*;

import play.db.jpa.*;
import play.data.validation.*;

@Entity
public class Thingy extends Model
{
    @Required
    public String Name;

    @ManyToOne
    public User Owner;

    public Thingy(String name, User owner)
    {
        this.Name = name;
        this.Owner = owner;
    }

    @Override
    public String toString()
    {
        return Name;
    }
}

还有这个模板表单

#{extends 'main.html' /}
#{set title:'Home' /}

<p>Current user = ${currentUser}</p>


#{form @saveThingy(), id:'saveThingy'}
    <input type="text" id="thingy.Name" name="thingy.Name"/>
    <input type="hidden" id="thingy.Owner" name="thingy.Owner" value="${currentUser}"/>
    <input type="submit" id="Save" value="Save"/>
#{/form}

控制器方法

public static void saveThingy(Thingy thingy)
{
    System.out.println("Name = " + thingy.Name);
    System.out.println("Owner = " + thingy.Owner);

    thingy.save();
}