code: @Override
  	public void removedService(
  			final ServiceReference<HttpService> serviceReference,
  			final HttpService service) {
  		LOG.debug("HttpService removed {}", serviceReference);
  		lock.lock();
  		HttpService removedHttpService = null;
  		try {
  			if (context != null) {
  				super.removedService(serviceReference, service);
  			}
  			if (httpService != service) {
  				return;
  			}
  			removedHttpService = httpService;
  			httpService = null;
  		} finally {
  			lock.unlock();
  		}
  		listener.unavailable(removedHttpService);
  	}
docs: Notify listeners that the http service became unavailable. Then looks for
  another one and if available notifies listeners.
  
  @see org.osgi.util.tracker.ServiceTracker#removedService(org.osgi.framework.ServiceReference, Object)