code: @Override
      public void removeEventListener(EventListener listener) {
          if (listener instanceof SessionListener) {
              sessionListeners.remove(listener);
          }
          if (listener instanceof SessionAttributeListener) {
              sessionAttributeListeners.remove(listener);
          }
      }
docs: Removes an event listener for for session-related events.
  
  @param listener the session event listener to remove
  @see #addEventListener(EventListener)