Index: locallib.php
===================================================================
RCS file: /cvsroot/moodle/moodle/mod/quiz/locallib.php,v
retrieving revision 1.105.2.6
diff -u -r1.105.2.6 locallib.php
--- locallib.php	31 Oct 2007 17:08:38 -0000	1.105.2.6
+++ locallib.php	4 Dec 2007 00:42:49 -0000
@@ -343,7 +343,7 @@
     static $cache = array();
     if (!array_key_exists($quizid, $cache)) {
         $cache[$quizid] = record_exists_select('quiz_feedback',
-                "quizid = $quizid AND feedbacktext <> ''");
+                "quizid = $quizid AND " . sql_isnotempty('quiz_feedback', 'feedbacktext', false, true));
     }
     return $cache[$quizid];
 }