我的 Laravel 应用程序出现了一些问题。我尝试制作 scraper，它看起来像这样。

<?php

namespace App\Http\Controllers;

use App\Scraper\Amazon;
use Illuminate\Http\Request;

class ScraperController extends Controller
{
    public $test;

    /**
     * Display a listing of the resource.
     *
     * @return \Illuminate\Http\Response
     */
    public function index()
    {
        $this->test = new Amazon();
       
        return $this->test;
    }

如您所见，我在应用程序内创建了名为 Scraper 的新文件夹，并且我有一个 Amazon.php 文件，如下所示：

<?php

namespace App\Scraper;

use Goutte\Client;

class Amazon
{
    public string $test = ''; 

    public function __construct()
    {
        return "test";
    }

    public function index()
    {
        $client = new Client();
        
        $crawler = $client->request('GET', 'https://www.amazon.co.uk/dp/B002SZEOLG/');

        $crawler->filter('#productTitle')->each(function ($node) {
            $this->test = $node->text()."\n";
        });

        return $this->test;
    }
}

并且它总是返回类似这样的错误

TypeError: Argument 1 passed to Symfony\Component\HttpFoundation\Response::setContent() must be of the type string or null, object given,

我做错了什么？