We uncovered this issue when working on
The MapR-DB table in question had 5 tablets with skewed data distribution (~6 million rows). A partial WIP fix for
DRILL-5394 caused the number of rows to be reported incorrectly (~300,000). 2 minor fragments were created (due to filter selectivity) for scanning the 5 tablets. And this resulted in an NPE, possibly related to an issue with assignment logic, that was now exposed.