If you call a non existing node using the content/view/full you'll get an 503 Service Unavailable error and php fatal error:

PHP Fatal error: Call to a member function attribute() on a non-object in /var/www/apache2php53/ezp5/app/ezpublish_testsystem/.run/kernel/classes/eznodeviewfunctions.php on line 553

Steps to reproduce

Call a non existing node using <your site>/content/view/full/59