Apache Release 5.0.1
5.01 fixed two issues:
PR 482: The HLL Union :: toString(), which prints out a simple diagnostic summary of the sketch, might change the internal state of the union. This was not intended.
PR 485: The KllItemsSketch<Boolean> was not serializing and deserializing the min and max values properly. It only affects this specific generic case of <Boolean>. This is a rather bizarre use case for quantiles -- but nonetheless it is fixed! :)