presto-main/src/main/java/io/prestosql/sql/planner/optimizations/PlanNodeDecorrelator.java/DecorrelatingVisitor/visitPlan
class DecorrelatingVisitor:        @Override
        protected Optional<DecorrelationResult> visitPlan(PlanNode node, Void context)
        {
            if (containsCorrelation(node, correlation)) {
                return Optional.empty();
            }
            return Optional.of(new DecorrelationResult(
                    node,
                    ImmutableSet.of(),
                    ImmutableList.of(),
                    ImmutableMultimap.of(),
                    false));
        }