code: private void _clearExecuteFlashMap(FacesContext facesContext)
      {
          Map<String, Object> map = _getExecuteFlashMap(facesContext);
  
          if (!map.isEmpty()) { //RTC 168417 / JIRA MYFACES-3975
              //JSF 2.2 invoke PreClearFlashEvent
              facesContext.getApplication().publishEvent(facesContext, 
                                                         PreClearFlashEvent.class, map);
          
              // Clear everything - note that because of naming conventions,
              // this will in fact automatically recurse through all children
              // grandchildren etc. - which is kind of a design flaw of SubKeyMap,
              // but one we're relying on
          
              // NOTE that we do not need a null check here, because there will
              // always be an execute Map, however sometimes an empty one!
              map.clear();
          }
      }
docs: Destroy the execute FlashMap, because it is not needed anymore.
  @param facesContext