docs: public Either<Throwable, V> oneOrError(final K key) {
          final ValueSubscriber<V> sub = ValueSubscriber.subscriber();
          return get(key).peek(a -> a.stream()
                                     .subscribe(sub))
                         .map(a -> sub.toEither())
                         .orElse(Either.left(new NoSuchElementException(
                                                                          "no adapter for key " + key)));
      }