code: @SuppressWarnings({ "unchecked", "rawtypes" })
      public Option<V> oneValue(final K key) {
          final ValueSubscriber<V> sub = ValueSubscriber.subscriber();
          return get(key).peek(a -> a.stream()
                                     .subscribe(sub))
                         .flatMap(a -> sub.toMaybe());
      }
docs: Extract one value from the selected pipe, if it exists
  
  @param key : Adapter identifier
  @return Maybe containing next value from the Adapter identified by the provided key