code: func NewComparablePrincipalSet(set policies.PrincipalSet) ComparablePrincipalSet {
  	var res ComparablePrincipalSet
  	for _, principal := range set {
  		cp := NewComparablePrincipal(principal)
  		if cp == nil {
  			return nil
  		}
  		res = append(res, cp)
  	}
  	return res
  }
docs: // NewComparablePrincipalSet constructs a ComparablePrincipalSet out of the given PrincipalSet