diff --git a/core/lib/Drupal/Core/Config/ConfigImporter.php b/core/lib/Drupal/Core/Config/ConfigImporter.php
index 389e5f6..2731d13 100644
--- a/core/lib/Drupal/Core/Config/ConfigImporter.php
+++ b/core/lib/Drupal/Core/Config/ConfigImporter.php
@@ -191,6 +191,8 @@ class ConfigImporter {
    * @param \Drupal\Core\Extension\ModuleExtensionList|null $extension_list_module
    *   The module extension list. This is left optional for BC reasons, but the
    *   optional usage is deprecated and will become required in Drupal 9.0.0.
+   *
+   * @todo Remove null default value https://www.drupal.org/node/2947083
    */
   public function __construct(StorageComparerInterface $storage_comparer, EventDispatcherInterface $event_dispatcher, ConfigManagerInterface $config_manager, LockBackendInterface $lock, TypedConfigManagerInterface $typed_config, ModuleHandlerInterface $module_handler, ModuleInstallerInterface $module_installer, ThemeHandlerInterface $theme_handler, TranslationInterface $string_translation, ModuleExtensionList $extension_list_module = NULL) {
     if ($extension_list_module === NULL) {