Error message

• Warning: Undefined array key "render element" in Drupal\Core\Theme\ThemeManager->render() (line 202 of core/lib/Drupal/Core/Theme/ThemeManager.php).
• Warning: Undefined array key "render element" in Drupal\Core\Theme\ThemeManager->render() (line 204 of core/lib/Drupal/Core/Theme/ThemeManager.php).