code: func (l Labels) Clone() Labels {
  	if l == nil {
  		return nil
  	}
  	out := make(Labels, len(l))
  	for key, vals := range l {
  		cvals := make([]string, len(vals))
  		copy(cvals, vals)
  		out[key] = cvals
  	}
  	return out
  }
docs: // Clone returns non-shallow copy of the labels set