java - エラー ValidationException: TraversableResolver.isReachable() の呼び出しで例外がスローされました

Question

データベースに接続する簡単なサインアップ フォームを作成しようとしたときに、このエラーが発生しました。Ubuntuを使用しています。これが私のコードです:

Signup.java

package controllers;

import models.User;
import play.data.Form;
import play.mvc.*;
import views.html.signup.*;
import views.html.*;

public class Signup extends Controller{
    public static Form<User> form = form(User.class);

    public static Result blank(){
        return ok(formsu.render(form));
    }
    public static Result submit(){
        Form<User> fillForm = form.bindFromRequest(); // Play mark this line !!!
        if(fillForm.hasErrors()) {
            return badRequest(formsu.render(fillForm));
        }
        else{
            User created = fillForm.get();
            return ok(result.render(created));
        }
    }
}

ユーザー.java

package models;

import java.util.List;

import javax.persistence.Entity;
import javax.validation.constraints.NotNull;

import play.data.validation.Constraints.Email;
import play.data.validation.Constraints.MinLength;
import play.data.validation.Constraints.Required;
import play.db.ebean.Model;


@Entity
public class User extends Model{
    @Required@NotNull@MinLength(6)
    public String username;

    @Required@NotNull@MinLength(6)
    public String password;

    @Required@Email
    public String email;

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

    public static Finder<Long, User> find = new Finder(Long.class, User.class);

    public static List<User> all(){
        return find.all();
    }
    public static void create(User user){
        user.save();
    }

}

formup.scala.html

@(user : Form[User])

@import helper._

@helper.form(action=routes.Signup.submit){
    @inputText(
        user("username"),
        '_label -> "Username",
        '_help -> "Put your username here"
    )

    @inputPassword(
        user("password"),
        '_label -> "Password",
        '_help -> "Put your password here"
    )

    @inputPassword(
        user("repeatpassword"),
        '_label -> "Repeat password",
        '_help -> "Put your password again"
    )

    @inputText(
        user("email"),
        '_label -> "Email",
        '_help -> "Put your email here"
    )

    <input type="submit" value="Sign up" />
}

ターミナルから:

--- (RELOAD) ---

[info] play - database [default] connected at jdbc:mysql://localhost/login
[info] play - Application started (Dev)
[error] application - 

! @6f07fm4f0 - Internal server error, for request [POST /signup] ->

play.core.ActionInvoker$$anonfun$receive$1$$anon$1: Execution exception [[ValidationException: Call to TraversableResolver.isReachable() threw an exception]]
    at play.core.ActionInvoker$$anonfun$receive$1.apply(Invoker.scala:134) [play_2.9.1.jar:2.0.4]
    at play.core.ActionInvoker$$anonfun$receive$1.apply(Invoker.scala:115) [play_2.9.1.jar:2.0.4]
    at akka.actor.Actor$class.apply(Actor.scala:318) [akka-actor.jar:2.0.2]
    at play.core.ActionInvoker.apply(Invoker.scala:113) [play_2.9.1.jar:2.0.4]
    at akka.actor.ActorCell.invoke(ActorCell.scala:626) [akka-actor.jar:2.0.2]
    at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:197) [akka-actor.jar:2.0.2]
Caused by: javax.validation.ValidationException: Call to TraversableResolver.isReachable() threw an exception
    at org.hibernate.validator.engine.ValidatorImpl.isValidationRequired(ValidatorImpl.java:1251) ~[hibernate-validator.jar:4.2.0.Final]
    at org.hibernate.validator.engine.ValidatorImpl.validateConstraint(ValidatorImpl.java:448) ~[hibernate-validator.jar:4.2.0.Final]
    at org.hibernate.validator.engine.ValidatorImpl.validateConstraintsForDefaultGroup(ValidatorImpl.java:397) ~[hibernate-validator.jar:4.2.0.Final]
    at org.hibernate.validator.engine.ValidatorImpl.validateConstraintsForCurrentGroup(ValidatorImpl.java:361) ~[hibernate-validator.jar:4.2.0.Final]
    at org.hibernate.validator.engine.ValidatorImpl.validateInContext(ValidatorImpl.java:313) ~[hibernate-validator.jar:4.2.0.Final]
    at org.hibernate.validator.engine.ValidatorImpl.validate(ValidatorImpl.java:139) ~[hibernate-validator.jar:4.2.0.Final]
Caused by: java.lang.RuntimeException: No @javax.persistence.Id field found in class [class models.User]
    at play.db.ebean.Model._idAccessors(Model.java:39) ~[play_2.9.1.jar:2.0.4]
    at play.db.ebean.Model._getId(Model.java:52) ~[play_2.9.1.jar:2.0.4]
    at play.db.ebean.Model.hashCode(Model.java:183) ~[play_2.9.1.jar:2.0.4]
    at org.hibernate.validator.engine.resolver.SingleThreadCachedTraversableResolver$TraversableHolder.buildHashCode(SingleThreadCachedTraversableResolver.java:153) ~[hibernate-validator.jar:4.2.0.Final]
    at org.hibernate.validator.engine.resolver.SingleThreadCachedTraversableResolver$TraversableHolder.<init>(SingleThreadCachedTraversableResolver.java:114) ~[hibernate-validator.jar:4.2.0.Final]
    at org.hibernate.validator.engine.resolver.SingleThreadCachedTraversableResolver$TraversableHolder.<init>(SingleThreadCachedTraversableResolver.java:96) ~[hibernate-validator.jar:4.2.0.Final]

"index" と "main" html は問題ありません :( 解決するのを手伝ってください。検索してみましたが、このエラーを修正できません。助けてくれてありがとう!!!