PersistentCollection未初始化，但数据库中的数据使用Symfony和Doctrine

I have a problem with a PersistentCollection.

I have an Object User (herited of FOSUserbundle user class) who have an EmdebedDocument Seance. The Seance have an Array of Event. My Seance Class:

/**
* @MongoDB\EmbeddedDocument
*/
class Seance
{
/**
 * @MongoDB\Id
 */
protected $id;

/**
 * @MongoDB\EmbedMany(targetDocument="Event")
 */
protected $dispos ;

/**
 * @MongoDB\Field(type="string")
 */
protected $rayonDeplacement;

/**
 * @MongoDB\Field(type="string")
 */
protected $lieu;

/**
 * @MongoDB\Field(type="string")
 */
protected $prix;

/**
 * @MongoDB\Field(type="string")
 */
protected $nbPersonne;

And my class Event

/**
* @MongoDB\EmbeddedDocument
*/
class Event extends BaseEvent
{
/**
 * @var integer
 * @MongoDB\Id
 */
protected $id;

/**
 * @var \DateTime
 * @MongoDB\Field(type="date")
 * @Assert\NotNull()
 */
protected $startDate;
/**
 * @var \DateTime
 * @MongoDB\Field(type="date")
 * @Assert\NotNull()
 */
protected $endDate;

I give the event from user with:

$user->getSeance()->getDispos()

This function returns a empty PersistentCollection while they are events in database.

When dump the return of getDispos() method I have:

I dont't understant why I have mongoData field with my data but arrayCollection empty.

Thank you for yout help.