code: func (c *Client) Close() error {
  	if cl, ok := c.sto.(io.Closer); ok {
  		return cl.Close()
  	}
  	if c := c.HTTPClient(); c != nil {
  		switch t := c.Transport.(type) {
  		case *http.Transport:
  			t.CloseIdleConnections()
  		case *http2.Transport:
  			t.CloseIdleConnections()
  		}
  	}
  	return nil
  }
docs: // Close closes the client.