diff --git a/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsTrait.php b/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsTrait.php
index 6e5294c..319e3a4 100644
--- a/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsTrait.php
+++ b/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsTrait.php
@@ -33,10 +33,9 @@
    *   HTML rendered content.
    */
   protected function getRenderedContent() {
-    $this->attachedAssets = new AttachedAssets();
     if (is_array($this->content)) {
       $html = \Drupal::service('renderer')->render($this->content);
-      $this->attachedAssets->createFromRenderArray($this->content);
+      $this->attachedAssets = AttachedAssets::createFromRenderArray($this->content);
       return $html;
     }
     else {