code: func SelectorFromSet(ls Set) Selector {
  	if ls == nil || len(ls) == 0 {
  		return internalSelector{}
  	}
  	var requirements internalSelector
  	for label, value := range ls {
  		r, err := NewRequirement(label, selection.Equals, []string{value})
  		if err == nil {
  			requirements = append(requirements, *r)
  		} else {
  			//TODO: double check errors when input comes from serialization?
  			return internalSelector{}
  		}
  	}
  	// sort to have deterministic string representation
  	sort.Sort(ByKey(requirements))
  	return requirements
  }
docs: // SelectorFromSet returns a Selector which will match exactly the given Set. A
  // nil and empty Sets are considered equivalent to Everything().