To clear an ESLint warning, add a @return annotation to the route() method in the mediawiki.router module.

Docs: https://doc.wikimedia.org/mediawiki-core/master/js/module-mediawiki.router.html#route
Code: https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/core/+/refs/heads/master/resources/src/mediawiki.router/router.js#133

To confirm that the warning is cleared, run npm install grunt and grunt lint, and ensure that no JSDoc warnings are reported for that file.