static void stop() {
    if (isStarted) {
      stopRefreshTimer();

      registry.stop();
      registry = null;
      releaseMBeanServer();// makes mbeanServer null
      isStarted = false;
    }
  }
Stops Registry, Refresh Timer. Releases Mbean Server after.
geode-core/src/main/java/org/apache/geode/admin/jmx/internal/MBeanUtils.java