docs: public void sendUpdateNotification(final SyndFeed feed) throws NotificationException {
          SyndLink hub = null;
          SyndLink self = null;
  
          for (final SyndLink link : feed.getLinks()) {
              if ("hub".equals(link.getRel())) {
                  hub = link;
              }
  
              if ("self".equals(link.getRel())) {
                  self = link;
              }
  
              if (hub != null && self != null) {
                  break;
              }
          }
  
          if (hub == null) {
              throw new NotificationException("A link rel='hub' was not found in the feed.");
          }
  
          if (self == null) {
              throw new NotificationException("A link rel='self' was not found in the feed.");
          }
  
          sendUpdateNotification(hub.getRel(), self.getHref());
      }