presto-main/src/main/java/io/prestosql/operator/EnforceSingleRowOperator.java/EnforceSingleRowOperatorFactory/EnforceSingleRowOperatorFactory
class EnforceSingleRowOperatorFactory:        public EnforceSingleRowOperatorFactory(int operatorId, PlanNodeId planNodeId)
        {
            this.operatorId = operatorId;
            this.planNodeId = requireNonNull(planNodeId, "planNodeId is null");
        }