Symfony VichUploaderBundle: File name could not be generated
<p>I am using VichUploader to upload files within a symfony project. In configuration i use (copied from documentation):</p>

<pre><code>service: vich_uploader.namer_property
options: { property: 'slug'}
</code></pre>

<p>In my entity i generate the slugs automatically with Gedmo/Sluggable:</p>

<pre><code>/**
 * @Gedmo\Slug(fields={"title"}, updatable=false)
 * @ORM\Column(type="string", length=100, nullable=false)
 */
protected $slug;
</code></pre>

<p>But when trying to save the entity i get the following error 500:</p>

<blockquote>
  <p>File name could not be generated: property slug is empty.</p>
</blockquote>

<p>If i set the property to 'title' it works. Did i forget a configuration parameter or something else to get it working with the Gedmo slug?</p>