code: def _update_content(sender, instance, created=None, **kwargs):
      
      if created: # a brand new FileUpload won't be referenced
          return
      for ref in FileUploadReference.objects.filter(upload=instance):
          try:
              obj = ref.content_object
              if obj:
                  obj.save()
          except AttributeError:
              pass
docs: Re-save any content models referencing the just-modified
      ``FileUpload``.
  
      We don't do anything special to the content model, we just re-save
      it. If signals are in use, we assume that the content model has
      incorporated ``render_uploads`` into some kind of rendering that
      happens automatically at save-time.