title: Symfony2 - Doctrine ArrayCollection methods coming back as undefined
body: <p>This is odd.  I have an entity that can contain an ArrayCollection of other, related entities.  When I make a couple of helper methods to allow me to add/retrieve the value of a singular entity, I get a Symfony2 exception telling me the method is not defined.  I'm including the namespace, so I'm at a loss as to what the problem is.  Code (names changed slightly due to a NDA) below:</p>
  
  <pre><code>namespace Acme\MyBundle\Entity;
  
  use Doctrine\ORM\Mapping as ORM;
  use Doctrine\Common\Collections\ArrayCollection;
  
  // ...
  
  public function setThing($thing)
  {
      $this-&gt;things-&gt;add($thing);
  }
  
  public function getThing()
  {
      return $this-&gt;things-&gt;current();
  }
  </code></pre>
  
  <p>What's really strange is that it's throwing the exception at <code>current()</code> but not <code>add()</code>:</p>
  
  <blockquote>
    <p>FatalErrorException: Error: Call to undefined method Acme\MyBundle\Entity\Thing::current() in /home/kevin/www/project/vendor/acme/my-bundle/Acme/MyBundle/Entity/MyEntity.php line 106</p>
  </blockquote>
  
  <p>Judging by the error, it looks like it's not treating <code>things</code> as an ArrayCollection.  Is there any way to force <code>things</code> to be an ArrayCollection?  I already have the following:</p>
  
  <pre><code>/**
   * @var ArrayCollection things
   *
   * @ORM\OneToMany(targetEntity="Thing", mappedBy="other")
   */
  private $things;
  </code></pre>
  
  <p>But I'm not sure what else to do.</p>