The code in this article no longer applies to latest sources. The AST part is not completed yet (default AST nodes), you have to build the nodes yourself. You are basically free to form your own node hierarchy.
Yes, token is not longer AST node; try directly casting the child, but it depends on how you form the current node:
value = this.ChildNodes;
It works only if you have a "constant" as your first node, but might not work if first child is some expression or some non-terminal - it really depends on your grammar.