Index.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Sales\Controller\Adminhtml\Creditmemo;

use Magento\Framework\App\Action\HttpGetActionInterface as HttpGetActionInterface;
use Magento\Sales\Controller\Adminhtml\Creditmemo\AbstractCreditmemo\Index as AbstractIndex;

class Index extends AbstractIndex implements HttpGetActionInterface
{
    /**
     * Index page
     *
     * @return \Magento\Backend\Model\View\Result\Page
     */
    public function execute()
    {
        return parent::execute();
    }
}