diff --git a/includes/migration.inc b/includes/migration.inc
index b50dbde..cea2cee 100644
--- a/includes/migration.inc
+++ b/includes/migration.inc
@@ -1166,7 +1166,8 @@ abstract class Migration extends MigrationBase {
       return $results;
     }
     else {
-      return reset($results);
+      $value = reset($results);
+      return empty($value) ? NULL : $value;
     }
   }