presto-parser/src/main/java/io/prestosql/sql/tree/DefaultTraversalVisitor.java/DefaultTraversalVisitor/visitFrameBound
class DefaultTraversalVisitor:    @Override
    public R visitFrameBound(FrameBound node, C context)
    {
        if (node.getValue().isPresent()) {
            process(node.getValue().get(), context);
        }

        return null;
    }