This did exactly what it said it would do, exactly what I needed it to do, and really saved me.

I have no idea how it happened but the "Page Not Found" page disappeared from the sitemap (presumably accidentally deleted) for a ConcreteCMS 5.8 site. The page_not_found.php file was still where it should be, but "Page Not Found" was gone from the sitemap.

This add-on got it back in place and use back in business.

Thank you.