code: 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);
    }
docs: Heapify the given srcMem into a Union object.
  @param <T> type of item
  @param srcMem the given srcMem.
  A reference to srcMem will not be maintained internally.
  @param comparator to compare items
  @param serDe an instance of ArrayOfItemsSerDe
  @return an instance of ItemsUnion