presto-main/src/main/java/io/prestosql/operator/GroupIdOperator.java/GroupIdOperator/GroupIdOperatorFactory
class GroupIdOperator:        public GroupIdOperatorFactory(
                int operatorId,
                PlanNodeId planNodeId,
                List<? extends Type> outputTypes,
                List<Map<Integer, Integer>> groupingSetMappings)
        {
            this.operatorId = operatorId;
            this.planNodeId = requireNonNull(planNodeId, "planNodeId is null");
            this.outputTypes = ImmutableList.copyOf(requireNonNull(outputTypes));
            this.groupingSetMappings = ImmutableList.copyOf(requireNonNull(groupingSetMappings));
        }