code: public void visit(final WebAppListener webAppListener) {
  		NullArgumentException.validateNotNull(webAppListener,
  				"Web app listener");
  		final EventListener listener = webAppListener.getListener();
  		if (listener != null) {
  			//CHECKSTYLE:OFF
  			try {
  				webContainer.unregisterEventListener(listener);
  			} catch (Exception ignore) {
  				LOG.warn("Unregistration exception. Skipping.", ignore);
  			}
  			//CHECKSTYLE:ON
  		}
  	}
docs: Unregisters listeners from web container.
  
  @throws NullArgumentException if listener is null
  @see WebAppVisitor#visit(WebAppListener)