presto-main/src/main/java/io/prestosql/sql/planner/ExpressionExtractor.java/ExpressionExtractor/extractExpressions
class ExpressionExtractor:    public static List<Expression> extractExpressions(PlanNode plan, Lookup lookup)
    {
        requireNonNull(plan, "plan is null");
        requireNonNull(lookup, "lookup is null");

        ImmutableList.Builder<Expression> expressionsBuilder = ImmutableList.builder();
        plan.accept(new Visitor(expressionsBuilder::add, true, lookup), null);
        return expressionsBuilder.build();
    }