Error in clean-sidebar feature #2474

The clean-sidebar feature is producing an error:

<img width="497" alt="Screenshot 2019-10-03 at 10 34 42" src="https://user-images.githubusercontent.com/478237/66116357-7c1de800-e5ca-11e9-9728-f7ebbddfd37f.png">

This seems to be happening in any issue or pull request page, e.g. here or here.

Refined Github version: 19.9.27