docs: public Future<V> oneOrErrorAsync(final K key, final Executor ex) {
          Future<V> res = Future.future();
          final CompletableFuture<Tuple0> cf = CompletableFuture.supplyAsync(() -> {
  
              final ValueSubscriber<V> sub = ValueSubscriber.subscriber();
              get(key).peek(a -> a.stream()
                      .subscribe(sub))
                      .map(a -> sub.toMaybe().fold(s -> {
                          res.complete(s);
                          return Tuple.empty();
                      }, () -> {
                          res.completeExceptionally(new NoSuchElementException());
                          return Tuple.empty();
                      }));
              return Tuple.empty();
  
  
          } , ex);
  
          return res;
      }