presto-main/src/main/java/io/prestosql/sql/planner/sanity/ValidateAggregationsWithDefaultValues.java/ValidateAggregationsWithDefaultValues/visitPlan
class ValidateAggregationsWithDefaultValues:        @Override
        protected Optional<SeenExchanges> visitPlan(PlanNode node, Void context)
        {
            return aggregatedSeenExchanges(node.getSources());
        }