code: public List<SystemEventListener> getListenersForEventClass(Class<? extends SystemEvent> eventClass) {
  
          if (eventClass == null) {
              throw new NullPointerException();
          }
          List<SystemEventListener> result = null;
          if (listenersByEventClass != null) {
              result = listenersByEventClass.get(eventClass);
          }
          return result;
  
      }
docs: <p class="changed_added_2_1">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 eventClass the <code>Class</code> of event for which the
  listeners must be returned.
  
  @throws NullPointerException if argument <code>eventClass</code> is <code>null</code>.
  
  @since 2.1