code: public List<ReferSubscriber> getRefererInfoByDialog(String dialogId) {
      List<ReferSubscriber> list = new ArrayList<>();
  
      synchronized (refererList) {
        for (ReferSubscriber s : refererList) {
          if (s.getDialogId().equals(dialogId)) {
            list.add(s);
          }
        }
      }
  
      return list;
    }
docs: Gets the subscription object(s) associated with the given dialog ID. The
  returned object(s) contains subscription state, received requests (NOTIFY's) and
  REFER/SUBSCRIBE responses, etc. for outbound REFER subscription(s) associated with the dialog.
  
  @param dialogId the dialog ID of interest
  @return ReferSubscriber object(s) associated with the dialog, or an empty list if there was
  never a refer subscription associated with that dialog.