code: func (c *Client) StreamVolumes(since *time.Time, output chan *ct.Volume) (stream.Stream, error) {
  	if since == nil {
  		s := time.Unix(0, 0)
  		since = &s
  	}
  	t := since.UTC().Format(time.RFC3339Nano)
  	return c.Stream("GET", "/volumes?since="+t, nil, output)
  }
docs: // StreamVolumes sends a series of Volume into the provided channel.
  // If since is not nil, only retrieves volume updates since the specified time.