public static void registerInstantiator() {
    Instantiator.register(new Instantiator(GemfireHttpSession.class, 27315) {
      @Override
      public DataSerializable newInstance() {
        return new GemfireHttpSession();
      }
    });
  }
This is set during serialization and then reset by the SessionManager when it is retrieved from
the attributes.
extensions/geode-modules-session-internal/src/main/java/org/apache/geode/modules/session/internal/filter/GemfireHttpSession.java