diff --git a/core/modules/locale/locale.compare.inc b/core/modules/locale/locale.compare.inc
index cb7fdb3..0dc9bd8 100644
--- a/core/modules/locale/locale.compare.inc
+++ b/core/modules/locale/locale.compare.inc
@@ -201,9 +201,13 @@ function _locale_translation_prepare_project_list($data, $type) {
  *   - "server_pattern": URI containing po file pattern.
  */
 function locale_translation_default_translation_server() {
-  $config = config('locale.settings');
+  $pattern = config('locale.settings')->get('translation.default_server_pattern');
+  // An additional check is required here. During the upgrade process
+  // config()->get() returns NULL. We use the defined value as fallback.
+  $pattern  = $pattern ? $pattern : LOCALE_TRANSLATION_DEFAULT_SERVER_PATTERN;
+
   return array(
-    'pattern' => $config->get('translation.default_server_pattern'),
+    'pattern' => $pattern,
   );
 }