code: public void unpublish(final WebApp webApp) {
  		NullArgumentException.validateNotNull(webApp, "Web app");
  		LOG.debug("Unpublishing web application [{}]", webApp);
  		final ServiceTracker<WebAppDependencyHolder, WebAppDependencyHolder> tracker = webApps
  				.remove(webApp);
  		if (tracker != null) {
  			tracker.close();
  		}
  	}
docs: Unpublish a web application.
  
  @param webApp web aplication to be unpublished
  @throws NullArgumentException if web app is null