code: @SuppressWarnings("unchecked")
    protected <R> void connect(final EtcdRequest<R> etcdRequest) throws IOException {
      this.connect(etcdRequest, etcdRequest.getPromise().getConnectionState());
    }
docs: Connect to server
  
  @param etcdRequest to request with
  @param <R>         Type of response
  @throws IOException if request could not be sent.