diff --git a/core/lib/Drupal/Core/Routing/Router.php b/core/lib/Drupal/Core/Routing/Router.php
index 4e603228e4..f98eb9b502 100644
--- a/core/lib/Drupal/Core/Routing/Router.php
+++ b/core/lib/Drupal/Core/Routing/Router.php
@@ -314,12 +314,12 @@ public function getRouteEnhancers() {
   protected function applyRouteFilters(RouteCollection $collection, Request $request) {
     // Route filters are expected to throw an exception themselves if they
     // end up filtering the list down to 0.
-    $filter_ids = NULL;
+    $filter_ids = [];
     foreach ($collection->all() as $route) {
       $filter_ids = array_merge($filter_ids, $route->getOption('_route_filters') ?: []);
     }
 
-    if (!isset($filter_ids)) {
+    if (empty($filter_ids)) {
       $filter_ids = $this->filterIds;
     }
     $filter_ids = array_unique($filter_ids);