title: Doctrine2 ManyToMany Self referencing
body: <p>I got problems with persisting many to many self referencing relations.
  I receive error: </p>
  
  <blockquote>
    <p>The class 'Doctrine\ORM\Persisters\ManyToManyPersister' was not found in the chain configured namespaces</p>
  </blockquote>
  
  <p>This happens when I remove all children form item saved with them.
  Leaving at least one don't make error happen. Also if I initially save entity with no children everything works fine.</p>
  
  <pre class="lang-php prettyprint-override"><code>/**
    * West\AlbumBundle\Entity\Album
    *
    * @ORM\Table(name="albums")
    * @ORM\Entity(repositoryClass="West\AlbumBundle\Entity\AlbumRepository")
    * @ORM\HasLifecycleCallbacks
    */
   class Album extends Entity implements CrudEntity
   {
  
       /**
        * @ORM\ManyToMany(targetEntity="Album")
        * @ORM\JoinTable(name="albums_relations",
        *         joinColumns={@ORM\JoinColumn(name="album_id", referencedColumnName="id")},
        *         inverseJoinColumns={@ORM\JoinColumn(name="related_album_id", referencedColumnName="id")}
        * ) 
        * @var ArrayCollection
        */
        protected $related_albums;
  }
  </code></pre>
  
  <p>If you're testing with Symfony2 forms remember to set</p>
  
  <blockquote>
    <p>"by_reference" => false</p>
  </blockquote>