diff --git a/core/lib/Drupal/Core/Menu/MenuLinkTree.php b/core/lib/Drupal/Core/Menu/MenuLinkTree.php
index a5ea3d2..2070b50 100644
--- a/core/lib/Drupal/Core/Menu/MenuLinkTree.php
+++ b/core/lib/Drupal/Core/Menu/MenuLinkTree.php
@@ -243,10 +243,12 @@ protected function buildItems(array $tree, CacheableMetadata &$tree_access_cache
       if ($data->access instanceof AccessResultInterface && !$data->access->isAllowed()) {
         continue;
       }
-      $element = array();
+      $element = [];
 
       // Set a variable for the <li>-tag. Only set 'expanded' true if the link
       // also has visible children within the current tree.
+      $element['is_expanded'] = FALSE;
+      $element['is_collapsed'] = FALSE;
       if ($data->hasChildren && !empty($data->subtree)) {
         $element['is_expanded'] = TRUE;
       }
@@ -254,6 +256,7 @@ protected function buildItems(array $tree, CacheableMetadata &$tree_access_cache
         $element['is_collapsed'] = TRUE;
       }
       // Set a helper variable to indicate whether link is in active trail.
+      $element['in_active_trail'] = FALSE;
       if ($data->inActiveTrail) {
         $element['in_active_trail'] = TRUE;
       }
diff --git a/core/modules/book/src/BookManager.php b/core/modules/book/src/BookManager.php
index 556350f..1db319c 100644
--- a/core/modules/book/src/BookManager.php
+++ b/core/modules/book/src/BookManager.php
@@ -548,6 +548,8 @@ protected function buildItems(array $tree) {
       // Set a class for the <li>-tag. Since $data['below'] may contain local
       // tasks, only set 'expanded' true if the link also has children within
       // the current book.
+      $element['is_expanded'] = FALSE;
+      $element['is_collapsed'] = FALSE;
       if ($data['link']['has_children'] && $data['below']) {
         $element['is_expanded'] = TRUE;
       }
@@ -556,6 +558,7 @@ protected function buildItems(array $tree) {
       }
 
       // Set a helper variable to indicate whether link is in active trail.
+      $element['in_active_trail'] = FALSE;
       if ($data['link']['in_active_trail']) {
         $element['in_active_trail'] = TRUE;
       }
diff --git a/core/modules/system/tests/src/Unit/Menu/MenuLinkTreeTest.php b/core/modules/system/tests/src/Unit/Menu/MenuLinkTreeTest.php
index 64d14b9..52bcce4 100644
--- a/core/modules/system/tests/src/Unit/Menu/MenuLinkTreeTest.php
+++ b/core/modules/system/tests/src/Unit/Menu/MenuLinkTreeTest.php
@@ -140,7 +140,7 @@ public function providerTestBuildCacheability() {
       ]
     ];
 
-    $get_built_element = function(MenuLinkTreeElement $element, array $classes) {
+    $get_built_element = function(MenuLinkTreeElement $element) {
       $return = [
         'attributes' => new Attribute(),
         'title' => $element->link->getTitle(),