return optional.isPresent() ? DoubleStream.of(optional.getAsDouble()) : DoubleStream.empty();
  }

  @SuppressWarnings("CatchingUnchecked") // sneaky checked exception
  private static void closeAll(BaseStream<?, ?>[] toClose) {
    // If one of the streams throws an exception, continue closing the others, then throw the
    // exception later. If more than one stream throws an exception, the later ones are added to the