presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/AddExchangesBelowPartialAggregationOverGroupIdRuleSet.java/AddExchangesBelowPartialAggregationOverGroupIdRuleSet/ndvIncludingNull
class AddExchangesBelowPartialAggregationOverGroupIdRuleSet:        private double ndvIncludingNull(SymbolStatsEstimate symbolStatsEstimate)
        {
            if (symbolStatsEstimate.getNullsFraction() == 0.) {
                return symbolStatsEstimate.getDistinctValuesCount();
            }
            return symbolStatsEstimate.getDistinctValuesCount() + 1;
        }