TWCS erroneously disabling tombstone compactions when unchecked_tombstone_compaction=true

This code:

this.options = new TimeWindowCompactionStrategyOptions(options);
if (!options.containsKey(AbstractCompactionStrategy.TOMBSTONE_COMPACTION_INTERVAL_OPTION) && !options.containsKey(AbstractCompactionStrategy.TOMBSTONE_THRESHOLD_OPTION))
{
disableTombstoneCompactions = true;
logger.debug("Disabling tombstone compactions for TWCS");
}
else
logger.debug("Enabling tombstone compactions for TWCS");
}

... in TimeWindowCompactionStrategy.java disables tombstone compactions in TWCS if you have not explicitly set either tombstone_compaction_interval or tombstone_threshold.  Adding 'tombstone_compaction_interval': '86400' to the compaction stanza in a table definition has the (to me unexpected) side effect of enabling tombstone compactions. 

This is surprising and does not appear to be mentioned in the docs.

I would suggest that tombstone compactions should be run unless these options are both set to 0.

If the concern is that (as with DTCS in CASSANDRA-9234) we don't want to waste time on tombstone compactions when we expect the tables to eventually be expired away, perhaps we should also check unchecked_tombstone_compaction and still enable tombstone compactions if that's set to true.

May also make sense to set defaults for interval & threshold to 0 & disable if they're nonzero so that setting non-default values, rather than setting ANY value, is what determines whether tombstone compactions are enabled?