docs: public static <T> ItemsUnion<T> getInstance(final Memory srcMem,
        final Comparator<? super T> comparator, final ArrayOfItemsSerDe<T> serDe) {
      final ItemsSketch<T> gadget = ItemsSketch.getInstance(srcMem, comparator, serDe);
      return new ItemsUnion<>(gadget.getK(), gadget.getComparator(), gadget);
    }