diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index dd032cb4cd0..8fc1e07544b 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -1192,7 +1192,7 @@ function bootstrap_hooks() {
 function drupal_unpack($obj, $field = 'data') {
   if ($obj->$field && $data = unserialize($obj->$field)) {
     foreach ($data as $key => $value) {
-      if (!isset($obj->$key)) {
+      if (!empty($key) && !isset($obj->$key)) {
         $obj->$key = $value;
       }
     }