public static List<URI> refIds(Collection<? extends RelatedResourceRep> refs){
  List<URI> ids=new ArrayList<URI>();
  if (refs != null) {
    for (    RelatedResourceRep ref : refs) {
      ids.add(ref.getId());
    }
  }
  return ids;
}

public static List < URI > refIds ( Collection < ? extends RelatedResourceRep > refs ) { List < URI > ids = new ArrayList < URI > ( ) ; if ( refs != null ) { for ( RelatedResourceRep ref : refs ) { ids . add ( ref . getId ( ) ) ; } } return ids ; }
gets a list of ids of data objects , null safe .
