Symfony2 Devrait argument de type “objet ou d'un tableau”, “string” compte tenu de

J'essaie désespérément de sauver le formulaire de l'entité de la Ville de OneToMany Anagrafic.
Je suis entré dans la "property_path" CityType la forme et j'ai renvoyé l'erreur,

Expected argument of type “object or array”, “string” given

Je ne comprends pas ce que je fais mal!

class Anagrafic
{
/**
 * @ORM\ManyToOne(targetEntity="City", inversedBy="anagrafics", cascade={"persist"})
 * @ORM\JoinColumn(name="city_id", referencedColumnName="id")
*/
private $city;
//..
//..
class City
{
/**
 * @ORM\OneToMany(targetEntity="Anagrafic", mappedBy="city", cascade={"persist"})
 */
private $anagrafics;
//...
//...
class CityType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder->add('comune', 'hidden', array('property_path' => 'city.id'))
//..
//..
class AnagraficType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder->add('city', new CityType())

EDIT: Désolé pour l'information incomplète, c'est l'exception:

CRITICAL - Symfony\Component\Form\Exception\UnexpectedTypeException: 
Expected argument of type "object or array", "string" given (uncaught exception) at
 /var/www/MyBusiness0_1/vendor/symfony/symfony/src/Symfony/Component/Form/Util/PropertyPath.php line 342 


/var/www/MyBusiness0_1/vendor/symfony/symfony/src/Symfony/Component/Form/Util/PropertyPath.php at line 342   
    for ($i = 0; $i <= $lastIndex; ++$i) {
        if (!is_object($objectOrArray) && !is_array($objectOrArray)) {
            throw new UnexpectedTypeException($objectOrArray, 'object or array');
        }
        $property = $this->elements[$i];

OriginalL'auteur Lughino | 2013-02-22