code: func (c *RPCClient) Ping() error {
  	var empty struct{}
  	return c.control.Call("Control.Ping", true, &empty)
  }
docs: // Ping pings the connection to ensure it is still alive.
  //
  // The error from the RPC call is returned exactly if you want to inspect
  // it for further error analysis. Any error returned from here would indicate
  // that the connection to the plugin is not healthy.