Probleme cake Email

Bonsoir,
Je suis actuellement en train de creer un formulaire d'inscription et j'ai un probleme lors de l'envoie du mail.
Mail :

Bonjour admin

Pour activer ce compte suivez ce lien :

Notice (8): Undefined variable: link [APP\View\Emails\html\signup.ctp, line 6]
Code Context

<p>Pour activer ce compte suivez ce lien : </p>

<p><?php echo $this->Html->link('Activer mon compte',$link); ?></p>
$viewFile = 'F:\wamp\www\2.7\app\View\Emails\html\signup.ctp'
$dataForView = array(
    'content' => '',
    'username' => 'admin',
    (int) 0 => array(
        'controller' => 'users',
        'action' => 'activate',
        (int) 0 => '33-a2b347966315bd7485521bab9984108b'
    )
)
$content = ''
$username = 'admin'
include - APP\View\Emails\html\signup.ctp, line 6
View::_evaluate() - CORE\Cake\View\View.php, line 971
View::_render() - CORE\Cake\View\View.php, line 933
View::render() - CORE\Cake\View\View.php, line 473
CakeEmail::_renderTemplates() - CORE\Cake\Network\Email\CakeEmail.php, line 1708
CakeEmail::_render() - CORE\Cake\Network\Email\CakeEmail.php, line 1561
CakeEmail::send() - CORE\Cake\Network\Email\CakeEmail.php, line 1171
UsersController::signup() - APP\Controller\UsersController.php, line 22
ReflectionMethod::invokeArgs() - [internal], line ??
Controller::invokeAction() - CORE\Cake\Controller\Controller.php, line 490
Dispatcher::_invoke() - CORE\Cake\Routing\Dispatcher.php, line 193
Dispatcher::dispatch() - CORE\Cake\Routing\Dispatcher.php, line 167
[main] - APP\webroot\index.php, line 118
/2.7/users/Activer mon compte
This email was sent using the CakePHP Framework

Mon UsersController :

<?php
class UsersController extends AppController{

    function signup(){
        if($this->request->is('post')){
            $d = $this->request->data;
            $d['User']['id'] = null;
            $d['User']['lastlogin'] = '2015-10-03 12:17:00';
            if(!empty($d['User']['password'])){
                $d['User']['password'] = Security::hash($d['User']['password'],'sha1',true);
            }
            if($this->User->save($d,true,array('username','password','mail'))){
                $link = array('controller'=>'users','action'=>'activate',$this->User->id.'-'.md5($d['User']['password']));
                App::uses('CakeEmail', 'Network/Email');
                $mail = new CakeEmail('default');
                $mail->from('noreply@localhost.com')
                    ->to($d['User']['mail'])
                    ->subject('Inscription')
                    ->emailFormat('html')
                    ->template('signup')
                    ->viewVars(array('username'=>$d['User']['username'],$link))
                    ->send();
                $this->Session->setFlash("Votre compte a bien été créé","notif");
            }else{
                $this->Session->setFlash("Merci de corriger vos erreurs","notif",array('type'=>'error'));
            }
        }
    }
}

signup.php :

<p>
<strong>Bonjour <?php echo $username; ?></strong>
</p>

<p>Pour activer ce compte suivez ce lien : </p>
<p><?php echo $this->Html->link('Activer mon compte',$link); ?></p>

Merci d'avance pour votre aide !