code: func AddFlashObj(overseer Overseer, w http.ResponseWriter, r *http.Request, key string, value interface{}) error {
  	mv, err := json.Marshal(value)
  	if err != nil {
  		return errors.Wrap(err, "unable to marshal flash value")
  	}
  
  	return AddFlash(overseer, w, r, key, string(mv))
  }
docs: // AddFlashObj adds a flash message to the session that will be deleted when it is retrieved with GetFlash