Index: modules/dblog/dblog.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/dblog/dblog.module,v
retrieving revision 1.55
diff -u -r1.55 dblog.module
--- modules/dblog/dblog.module	1 Sep 2010 03:03:05 -0000	1.55
+++ modules/dblog/dblog.module	11 Sep 2010 23:48:23 -0000
@@ -127,9 +127,14 @@
  * Note some values may be truncated for database column size restrictions.
  */
 function dblog_watchdog(array $log_entry) {
+  $user_uid = 0;
+  if (isset($log_entry['user']->uid)) {
+    $user_uid = $log_entry['user']->uid;
+  }
+
   Database::getConnection('default', 'default')->insert('watchdog')
     ->fields(array(
-      'uid' => $log_entry['user']->uid,
+      'uid' => $user_uid,
       'type' => substr($log_entry['type'], 0, 64),
       'message' => $log_entry['message'],
       'variables' => serialize($log_entry['variables']),