@Override
 public boolean apply(AtomicReference<Instance> input) {
   Instance response = resources.instance(input.get().selfLink());
   if (response == null) {
     return false;
   }
   input.set(response);
   return true;
 }
 @Override
 public Instance getNode(String selfLink) {
   return resources.instance(URI.create(checkNotNull(selfLink, "id")));
 }