code: func (v *HistogramVec) MustCurryWith(labels Labels) ObserverVec {
  	vec, err := v.CurryWith(labels)
  	if err != nil {
  		panic(err)
  	}
  	return vec
  }
docs: // MustCurryWith works as CurryWith but panics where CurryWith would have
  // returned an error.