diff --git a/core/lib/Drupal/Core/Config/Config.php b/core/lib/Drupal/Core/Config/Config.php
index 91d7695006..17010baef6 100644
--- a/core/lib/Drupal/Core/Config/Config.php
+++ b/core/lib/Drupal/Core/Config/Config.php
@@ -307,12 +307,14 @@ public function getOriginal($key = '', $apply_overrides = TRUE) {
    * Determines if overrides are applied to a key for this configuration object.
    *
    * @param string $key
-   *   A string that maps to a key within the configuration data.
+   *   (optional) A string that maps to a key within the configuration data. If
+   *    not supplied TRUE will be returned if there are any overrides at all for
+   *    this configuration object.
    *
    * @return bool
    *   TRUE if there are any overrides for the key, otherwise FALSE.
    */
-  public function hasOverrides($key = '') {
+  public function hasOverrides($key = NULL) {
     if ($key) {
       $parts = explode('.', $key);
       $override_exists = FALSE;