Laravel SQLSTATE [23000]:完整性约束违规:1062重复条目

我是Laravel的新手,这是我在Laravel的第一个项目.像往常一样,我首先要开发一个完整的用户身份验证系统.我可以注册一个用户,可以发送用户验证邮件,点击该链接后我可以激活一个新的用户帐户,可以登录并可以注销.但是,当我尝试注册另一个新用户并点击验证链接后,我面临一个例外,即,

Illuminate \ Database \ QueryException
SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '' for key     'users_code_unique' (SQL: update `users` set `code` = , `active` = 1, `updated_at` = 2014-07-   25 04:26:06 where `id` = 41)

现在这是我的route.php,

'home',
     'uses' =>'HomeController@index'
     ));

Route::get('/signin',array(
    'as'        =>'signin',
    'uses'      =>'AccountController@signinGet'
    ));

Route::get('/signup',array(
    'as' => 'signup',
    'uses' => 'AccountController@signupGet'
    ));

/* 

/* 
/Authenticated Group
*/
 Route::group(array('before' => 'auth'),function(){
 /* 
 /Sign Out(GET)
*/

 Route::get('/signout',array
    (
        'as' => 'signout',
        'uses' => 'AccountController@signoutGet'
    ));

 });

/* 
/UnAuthenticated Group
*/
Route::group(array('before' => 'guest'),function(){

/* CSRF Protect*/
Route::group(array('before' => 'csrf'),function(){
        /*
        / Create Account(POST)
        */
        Route::post('/signup',array(
                'as'=> 'signup',
                'uses'=>'AccountController@signupPost'
            ));

        /*
        / Sign In(POST)
        */

        Route::post('/signin',array(
                'as' => 'signin-post',
                'uses' => 'AccountController@signinPost'
            ));
 });

 /* 
 / Sign In (GET) 
 */

 Route::get('/signin',array(
        'as' => 'signin',
        'uses' => 'AccountController@signinGet'
    ));

 /* 
 /Create Account(GET) 
 */
 Route::get('/signup',array(
        'as' => 'signup',
        'uses'=> 'AccountController@signupGet'
    ));
 Route::get('signup/account/activate/{code}',array(
        'as'        =>'activate-account',
        'uses'      =>'AccountController@activatePost'
    ));
 });
 ?>

这是我的AccountController

 'required|email',
            'password' => 'required'
        ));

    if($validator->fails()){
        //redirect to the signin page
        return Redirect::route('signin')
                ->withErrors($validator)
                ->withInput();
    }else{
        //Attempt user singin

        $auth = Auth::attempt(array
            (
                'email' => Input::get('email'),
                'password' => Input::get('password'),
                'active' => 1
            ));

        if($auth){
            //Redirect To intented URL
            return Redirect::intended('/');
        }
        else
        {

            return Redirect::route('signin')
                                ->with('global','The username or password you provided is wrong or account not activated!');
        }

    }

            return Redirect::route('signin')    
                                ->with('global','There is a problem Signing You in.');
}


/**
 * Show the form for creating a new resource.
 *
 * @return Response
 */

public function signupGet()
{
    return View::make('account.signup');
}

public function signupPost()
{
    $validator = Validator::make(Input::all(), array(

        'email'             => 'required|max:255|email|unique:users',
        'username'          => 'required|min:3|unique:users',
        'password'          => 'required|min:6',
        'password_again'    =>  'required|same:password'

        )
    );

    if($validator->fails())
    {
        return Redirect::route('signup')
            ->withErrors($validator)
            ->withInput();
    }else
    {
        $email          = Input::get('email');
        $username       = Input::get('username');
        $password       = Input::get('password');

        //Activation Code
        $code = str_random(60);

        $user = User::create(array(
                    'email'     => $email,
                    'username'  => $username,
                    'password'  => Hash::make($password),
                    'code'      => $code,
                    'active'    => 0                
                    )
        );

        if($user){
            //User Activation Code Creation
            Mail::send('emails.auth.activate', array('link' => URL::route('activate-account',$code), 'username' => $username),function($message) use ($user)
                {
                    $message->to($user->email,$user->username)->subject('Activate Your Account');
                });

            return Redirect::route('signup')
                            ->with('global','Your Account has been created! We have sent you an email to activate your account.Please Check the both the Inbox and Spam Folder.');

        }

    }


    //return 'This is a Post Result';
}

public function activatePost($code){

    $user = User::where('code','=',$code)->where('active','=',0);
    if($user->count()){
        $user = $user->first();

        $user->active = 1;
        $user->code = '';
        if($user->save()){
            return Redirect::route('home')
                            ->with('global','Activated!.You can sign in now!'); 
        }
    }

    else{
        return Redirect::route('signup')
                        ->with('global','Sorry!We could not activate your acount,please try again later.');
    }
}


public function signoutGet(){

    Auth::logout();
    return Redirect::route('home');
}
}
?>

这是我的创建用户迁移文件

increments('id');
        $table->string('username',255)->unique();
        $table->string('email',255)->unique();
        $table->string('password',60);
        $table->string('password_temp',60);
        $table->string('code',60)->unique();
        $table->integer('active');
        $table->timestamps();
    });
}

/**
 * Reverse the migrations.
 *
 * @return void
 */
public function down()
{
    Schema::drop('users');
}

}
?>

这是我的user.php

remember_token;
    }

    public function setRememberToken($value)
    {
        $this->remember_token = $value;
    }

    public function getRememberTokenName()
    {
        return 'remember_token';
    }

protected $fillable = array('email','username','password','password_temp','code','active');

use UserTrait, RemindableTrait;

/**
 * The database table used by the model.
 *
 * @var string
 */
protected $table = 'users';



/**
 * The attributes excluded from the model's JSON form.
 *
 * @var array
 */
protected $hidden = array('password', 'remember_token');

}
?>

现在问题是什么？