I'm not familiar with the reasons why `aval.types` would be undefined here. One example I found where it is undefined is when running `bin/condense --plugin node --plugin doc_comment markdown.js` where markdown.js is https://github.com/evilstreak/markdown-js/blob/368b33a24213908499db831e1545de7fe3abe4e5/lib/markdown.js#L1571. It fails at line 1571:

```javascript
        // add in the href and title, if present
        attrs.href = ref.href;
```


This falsey check fixes the issue, but it might mask other bugs.