docs: public static void main(String[] args) throws Exception {
      CustomHeaderClient client = new CustomHeaderClient("localhost", 50051);
      try {
        /* Access a service running on the local machine on port 50051 */
        String user = "world";
        if (args.length > 0) {
          user = args[0]; /* Use the arg as the name to greet if provided */
        }
        client.greet(user);
      } finally {
        client.shutdown();
      }
    }