code: func AddFromGatherer(job string, grouping map[string]string, url string, g prometheus.Gatherer) error {
  	return push(job, grouping, url, g, "POST")
  }
docs: // AddFromGatherer works like FromGatherer, but only previously pushed metrics
  // with the same name (and the same job and other grouping labels) will be
  // replaced. (It uses HTTP method 'POST' to push to the Pushgateway.)
  //
  // Deprecated: Please use a Pusher created with New instead.