When Emacs Slack Fails Because of a Link to a Unavailable Channel

(cl-defmethod slack-block-to-string ((this slack-rich-text-channel-element) option)
  (let ((team (plist-get option :team))
        (id (oref this channel-id)))
    (unless team
      (error "`slack-rich-text-channel-element' need team as option"))

    (let (
          (room (slack-room-find id team))
          )
      (propertize (format "#%s" (if room
                                    (slack-room-name room team)
                                  " broken link because unavailable"
                                  )
                          )
                  'room-id id
                  'keymap slack-channel-button-keymap
                  'face 'slack-channel-button-face)
      )
    )
  )