Errors when a module has been removed but not uninstalled

1. Install the mod_certificate module
2. Enable the activitynames filter in a course
3. Add a certificate the course called 'chocolate'
4. add a label to the course with the text 'eating chocolate'
5. VERIFY: that the activity names filter has auto-linked the activity (if not, its more likely to be misconfig, not a problem with this issue)
6. Remove the mod_certificate files from disk (but don't uninstall it)
7. Purge caches
8. View the course page
9. VERIFY: there is not a notice 'Notice: Undefined property: stdClass::$name in /Users/danp/moodles/pm/moodle/lib/modinfolib.php on line 495'

In filter/activitynames/filter.php amend as follows:

function filter_activitynames_comparemodulenamesbylength($a, $b)
{
if (!isset($a->name)) return 1;
if (!isset($b->name)) return -1;
// No need for 0 condition as empty string should be at bottom of heap.
if (strlen($a->name) == strlen($b->name))

return (strlen($a->name) < strlen($b->name)) ? 1 : -1;
}