code: public static <T> @NonNull CompletableFuture<Optional<T>> emptyOptionalFuture() {
      return CompletableFuture.completedFuture(Optional.empty());
    }
docs: Returns a completable future that is completed with an {@link Optional#empty() empty Optional}.
  
  @param <T> the type
  @return a completable future that is completed with an empty Optional