Symfony2 - simplecms : how add extras data?

I've a problem in my form for the entity Page from simplecmsI want to add an item in the array Extras, so i added it in my formtype :

use Symfony\Component\Form\AbstractType;use Symfony\Component\Form\FormBuilderInterface;use Symfony\Cmf\Bundle\SimpleCmsBundle\Doctrine\Phpcr\Page;class PageType extends AbstractType{    public function buildForm(FormBuilderInterface $builder, array $options)    {        $builder->add('title', 'text', array('label' => 'Titre','attr' => array('placeholder' => 'Titre complet de la page')            ))        ->add('name', 'text', array('label' => 'Label','attr' => array('placeholder' => 'nom-simplifie-de-la-page')            ))        ->add('body', 'ckeditor')        ->add('locale', 'hidden')        ->add('publishable')            ->add('extras_link','text', array('property_path' =>"extras['link']",            ));                        }

The vars are in class Page (i didnt had to override it) and functions removeExtra() and addExtra() too (necessary to my form alimentation)

/** * Add a single key - value pair to extras * * @param string $key  * @param string $value - if this is not a string it is cast to one */public function addExtra($key, $value){    $this->extras[$key] = (string) $value;}/** * Remove a single key - value pair from extras, if it was set. * * @param string $key */public function removeExtra($key){    if (array_key_exists($key, $this->extras)) {        unset($this->extras[$key]);    }}

form is working, but when i submit, it find removeExtra() but not addExtra()

"Found the public method "removeExtra()", but did not find a public "addExtra()" on class Symfony\Cmf\Bundle\SimpleCmsBundle\Doctrine\Phpcr\Page"

Somebody already had this problem? or know how to add data in extras?THX (sorry for my english)