docs: public Deferred<ArrayList<Object>> shutdown() {
      // Clear shared instance.
      INSTANCE.set(null);
  
      final Collection<Deferred<Object>> deferreds = Lists.newArrayList();
  
      if (http_plugin_commands != null) {
        for (final Map.Entry<String, HttpRpcPlugin> entry : http_plugin_commands.entrySet()) {
          deferreds.add(entry.getValue().shutdown());
        }
      }
  
      if (rpc_plugins != null) {
        for (final RpcPlugin rpc : rpc_plugins) {
          deferreds.add(rpc.shutdown());
        }
      }
  
      return Deferred.groupInOrder(deferreds);
    }