Search does not work on 404 page

[Legioth]

Opening https://vaadin.com/docs/v15/flow/typescript/creating-routes.html (which is linked to through vaadin/flow#16209) leads to a 404 page with JavaScript errors that seem to prevent the search functionality from working.

[jouni]

This is the error that breaks the search (and all other client-side/SPA functionality):