code: private void processFlash(RouteContext routeContext) {
          Flash flash = null;
  
          if (routeContext.hasSession()) {
              // get flash from session
              flash = routeContext.removeSession("flash");
              // put an empty flash (outgoing flash) in session; defense against session.get("flash")
              routeContext.setSession("flash", new Flash());
          }
  
          if (flash == null) {
              flash = new Flash();
          }
  
          // make current flash available to templates
          routeContext.setLocal("flash", flash);
      }
docs: Removes a Flash instance from the session, binds it to the RouteContext,
  and creates a new Flash instance.
  
  @param routeContext