presto-parser/src/main/java/io/prestosql/sql/tree/StackableAstVisitor.java/StackableAstVisitorContext/getPreviousNode
class StackableAstVisitorContext:        public Optional<Node> getPreviousNode()
        {
            if (stack.size() > 1) {
                return Optional.of(stack.get(1));
            }
            return Optional.empty();
        }