title: validation.yml not working wit image file
body: <p>i read <a href="http://symfony.com/doc/current/reference/constraints/Image.html" rel="nofollow">this documentation</a> about this issue </p>
  
  <p>but not working</p>
  
  <p>and return this error: </p>
  
  <blockquote>
    <p>The controller must return a response (null given). Did you forget to add a return statement somewhere in your controller?</p>
  </blockquote>
  
  <p>mi code is </p>
  
  <p>in  <strong>MyApp\MainBundle\Resources\config\validation.yml</strong></p>
  
  <p>MyApp\MainBundle\Entity\Product:</p>
  
  <pre><code>properties:
      name: # YES VALIDATE
          - Length:
              min: 2
              max: 60
      image: # NOT VALIDATE 
          - Image:
              maxSize: 6000000
              mimeTypes: [image/*]
              mimeTypesMessage: Solo imagenes estan permitidas
  </code></pre>
  
  <p>the <strong>Entity MyApp\MainBundle\Entity\Product</strong></p>
  
  <pre><code>use Symfony\Component\HttpFoundation\File\File;
  
  /**
   * @ORM\Column(name="image", type="string", length=255, nullable=false)
   */
  private $image;
  
  
  // UPLOAD OF IMAGES   
  
  /**
   * Set image
   */
  public function setImage(File $image= null)
  {
      $this-&gt;image = $image;
      return $this;
  }
  
  /**
   * Get image
   *
   * @return UploadedFile 
   */
  public function getImage()
  {
      return $this-&gt;image;
  }
  
  
  // UPLOAD  IMAGES    
  /**
  * @ORM\PrePersist()
  */
  public function prePersist()
  {        
      ## .....
  }
  
  /**
   * @ORM\PreUpdate()
   */
  public function preUpdate()
  { 
      ## .....
  }
  
  ## ETC .....  
  </code></pre>