An existing Differential on my site was updated, and now it is displaying...
> Unhandled Exception ("InvalidArgumentException")
> Argument 2 passed to phutil_implode_html() must be of the type array, string given, called in /home/hawksnest/phab/phabricator/src/infrastructure/diff/view/PHUIDiffTableOfContentsItemView.php on line 277 and defined
All the other Differentials are working fine.