presto-main/src/main/java/io/prestosql/sql/planner/planprinter/PlanPrinter.java/PlanPrinter/visitGroupReference
class PlanPrinter:        @Override
        public Void visitGroupReference(GroupReference node, Void context)
        {
            addNode(node, "GroupReference", format("[%s]", node.getGroupId()), ImmutableList.of());

            return null;
        }