presto-main/src/main/java/io/prestosql/sql/planner/iterative/Plans.java/Plans/visitPlan
class Plans:        @Override
        protected PlanNode visitPlan(PlanNode node, Void context)
        {
            List<PlanNode> children = node.getSources().stream()
                    .map(child -> child.accept(this, context))
                    .collect(Collectors.toList());

            return node.replaceChildren(children);
        }