A call to e.g. /wp-json/wp/v2/posts/123456 where post 123456 doesn't exist returns an error:
Notice: Undefined property: stdClass::$show_in_rest in /srv/www/rooftop-cms/public/web/app/mu-plugins/rest-api/lib/endpoints/class-wp-rest-posts-controller.php on line 858
A call to e.g. /wp-json/wp/v2/posts/123456 where post 123456 doesn't exist returns an error:
It should just return a 404 instead.