code: func MustNewConstSummary(
  	desc *Desc,
  	count uint64,
  	sum float64,
  	quantiles map[float64]float64,
  	labelValues ...string,
  ) Metric {
  	m, err := NewConstSummary(desc, count, sum, quantiles, labelValues...)
  	if err != nil {
  		panic(err)
  	}
  	return m
  }
docs: // MustNewConstSummary is a version of NewConstSummary that panics where
  // NewConstMetric would have returned an error.