Fix #11132 - trim warning in Cake\View\Helper::addClass

src/View/Helper.php

@@ -197,7 +197,9 @@ class Helper implements EventListenerInterface
      */
     public function addClass(array $options = [], $class = null, $key = 'class')
     {
-        if (isset($options[$key]) && trim($options[$key])) {
+        if (is_array($options[$key])) {
+            $options[$key][] = $class;
+        } else if (isset($options[$key]) && trim($options[$key])) {
             $options[$key] .= ' ' . $class;
         } else {
             $options[$key] = $class;