diff -ur orig/drupal-6.3/includes/common.inc patched/drupal-6.3/includes/common.inc
--- orig/drupal-6.3/includes/common.inc	2008-07-09 17:48:27.000000000 -0400
+++ patched/drupal-6.3/includes/common.inc	2008-07-10 12:12:07.000000000 -0400
@@ -3150,9 +3150,12 @@
   if (!is_null($table) && isset($schema[$table])) {
     return $schema[$table];
   }
-  else {
+  elseif (is_array($schema)) {
     return $schema;
   }
+  else {
+    return array();
+  }
 }
 
 /**