Use array_key_last()

- see OpenMage#4111 (comment)

Author: sreichel

app/code/core/Mage/Adminhtml/Block/Page/Menu.php

@@ -164,10 +164,9 @@ protected function _buildMenuArray(Varien_Simplexml_Element $parent, $path = '',
 
         uasort($parentArr, [$this, '_sortMenu']);
 
-        foreach (array_keys($parentArr) as $key) {
-            $last = $key;
-        }
-        if (isset($last)) {
+        $last = array_key_last($parentArr);
+
+        if (!is_null($last)) {
             $parentArr[$last]['last'] = true;
         }
 

app/code/core/Mage/Adminhtml/Model/System/Config/Source/Admin/Page.php

@@ -109,10 +109,9 @@ protected function _buildMenuArray(?Varien_Simplexml_Element $parent = null, $pa
 
         uasort($parentArr, [$this, '_sortMenu']);
 
-        foreach (array_keys($parentArr) as $key) {
-            $last = $key;
-        }
-        if (isset($last)) {
+        $last = array_key_last($parentArr);
+
+        if (!is_null($last)) {
             $parentArr[$last]['last'] = true;
         }