@SuppressWarnings("unchecked") public <T>void addAttribute(Key<List<T>> key,T value){
  List<T> list=getAttribute(key);
  if (list == null) {
    list=Lists.newArrayList();
    putAttribute(key,list);
  }
  list.add(value);
}

@ SuppressWarnings ( "unchecked" ) public < T > void addAttribute ( Key < List < T > > key , T value ) { List < T > list = getAttribute ( key ) ; if ( list == null ) { list = Lists . newArrayList ( ) ; putAttribute ( key , list ) ; } list . add ( value ) ; }
adds an attribute value .
