docs: def portrait_image(model, request):
      """XXX: needs polishing. Return configured default portrait if not set
      on user.
      """
      response = Response()
      cfg = ugm_general(model)
      response.body = model.attrs[cfg.attrs['users_portrait_attr']]
      response.headers['Content-Type'] = 'image/jpeg'
      response.headers['Cache-Control'] = 'max-age=0'
      return response