code: public List<SystemEventListener> getViewListenersForEventClass(Class<? extends SystemEvent> systemEvent) {
  
          if (systemEvent == null) {
              throw new NullPointerException();
          }
          if (viewListeners != null) {
              return viewListeners.get(systemEvent);
          }
          return null;
          
      }
docs: <p class="changed_added_2_0">Return the
  <code>SystemEventListener</code> instances registered on this
  <code>UIComponent</code> instance that are interested in events
  of type <code>eventClass</code>.</p>
  
  @param systemEvent the <code>Class</code> of event for which the
  listeners must be returned.
  
  @throws NullPointerException if argument <code>systemEvent</code>
  is <code>null</code>.
  
  @since 2.0