presto-main/src/main/java/io/prestosql/sql/planner/plan/StatisticAggregations.java/StatisticAggregations/Parts
class StatisticAggregations:        public Parts(StatisticAggregations partialAggregation, StatisticAggregations finalAggregation, Map<Symbol, Symbol> mappings)
        {
            this.partialAggregation = requireNonNull(partialAggregation, "partialAggregation is null");
            this.finalAggregation = requireNonNull(finalAggregation, "finalAggregation is null");
            this.mappings = ImmutableMap.copyOf(requireNonNull(mappings, "mappings is null"));
        }