title: FileNotFoundError inside a celery task
body: <p>I have a celery task that operate with file from Django model</p>
  <pre class="lang-py prettyprint-override"><code>class Something(models.Model):
      doc = models.FileField()
  
  @app.task
  def operate_with_file(instance_id: int):
      instance = Something.objects.get(id=instance_id)
      size = instance.doc.file.size
  </code></pre>
  <p>When celery worker run this task i got error FileNotFoundError on string <code>size = instance.doc.file.size</code>. If i call <code>operate_with_file </code> manually from django shell that works fine. File already exists in a model. What wrongs with this?</p>