@fb55 is correct: if `this` were the root node, then `this.parents()` would return an empty set, `this.parents.last()` would likewise be an empty set, and `this.parents().last()[0]` would be `undefined`, resulting in a reference error.

This cannot occur since this codepath is only taken for elements whose `type` attribute is `radio`. From [lines 70 & 71](https://github.com/jugglinmike/cheerio/blob/05d2eca3f5bfa0c91f24614bb0ff2d2e71c1674a/lib/api/attributes.js#L70):

```javascript
switch (this.attr('type')) {
  case 'radio':
    // the change we're discussing
```