code: @SuppressWarnings("unchecked")
      protected void flash(String name, Object value) {
          checkFlasher();
          ((Map) session().get("flasher")).put(name, value);
      }
docs: Sends value to flash. Flash survives one more request.  Using flash is typical
  for POST/GET pattern,
  
  @param name name of value to flash
  @param value value to live for one more request in current session.