Laravel Socialite 4.1.0でのエラー

Laravel初心者です。

Laravel 5.7.28
XAMPP
Socialite 4.1.0

でOAuth認証を実装しようと考え、下記サイトを参考にしました。

https://leben.mobi/blog/laravel5_social_login/php/

一通りサイトに習いコードを記述しましたが、ソーシャルボタンを押下時に下記エラーが発生します。

Symfony \ Component \ Debug \ Exception \ FatalThrowableError (E_RECOVERABLE_ERROR)
Argument 1 passed to Laravel\Socialite\SocialiteManager::formatRedirectUrl() must be of the type array, null given, called in C:\xampp\htdocs\demo\vendor\laravel\socialite\src\SocialiteManager.php on line 126

エラー箇所は下記のようです。
C:\xampp\htdocs\demo\vendor\laravel\socialite\src\SocialiteManager.php

     *
     * @param  array  $config
     * @return array
     */
    public function formatConfig(array $config)
    {
        return array_merge([
            'identifier' => $config['client_id'],
            'secret' => $config['client_secret'],
            'callback_uri' => $this->formatRedirectUrl($config),
        ], $config);
    }
 
    /**
     * Format the callback URL, resolving a relative URI if needed.
     *
     * @param  array  $config
     * @return string
     */
    protected function formatRedirectUrl(array $config)
    {
        $redirect = value($config['redirect']);
 
        return Str::startsWith($redirect, '/')
                    ? $this->app['url']->to($redirect)
                    : $redirect;
    }
 
    /**
     * Get the default driver name.
     *
     * @throws \InvalidArgumentException
     *

原因がわからず困っております。
ご教授よろしくお願いします。

追記:
SocialiteManager.php 126行付近

    public function buildProvider($provider, $config)
    {
        return new $provider(
            $this->app['request'], $config['client_id'],
            $config['client_secret'], $this->formatRedirectUrl($config),
            Arr::get($config, 'guzzle', [])
        );
    }

config/services.php

    'google' => [
      'client_id'     => env('**********************************************************'),
      'client_secret' => env('*************************'),
      'redirect'      => env('**************************'),
    ],

config/app.php

'providers' => [
Laravel\Socialite\SocialiteServiceProvider::class,
],
'aliases' => [
    'Socialite'  => Laravel\Socialite\Facades\Socialite::class,
],

Auth/LoginController.php

<?php

namespace App\Http\Controllers\Auth;

use Illuminate\Http\Request;
use App\Http\Controllers\Controller;
use Illuminate\Foundation\Auth\AuthenticatesUsers;
use App\Events\Logined;
use Socialite;
use App\User;
use Auth;


class LoginController extends Controller
{
    /*
    |--------------------------------------------------------------------------
    | Login Controller
    |--------------------------------------------------------------------------
    |
    | This controller handles authenticating users for the application and
    | redirecting them to your home screen. The controller uses a trait
    | to conveniently provide its functionality to your applications.
    |
    */

    use AuthenticatesUsers;
    protected $maxAttempts = 2;     // ログイン試行回数（回）
    protected $decayMinutes = 10;   // ログインロックタイム（分）
    /**
     * Where to redirect users after login.
     *
     * @var string
     */
    protected $redirectTo = '/verified';

    /**
     * Create a new controller instance.
     *
     * @return void
     */
    public function __construct()
    {
        $this->middleware('guest')->except('logout');
    }

    /**
     * ログイン認証後の処理
     * @param Request $request
     * @param $user
     */
    protected function authenticated(Request $request, $user)
    {
        // ログインイベントを発火させ最終ログイン日時を記録する
        event(new Logined());
    }

    public function username()
    {
        return 'userid';
    }

   /**
    * Handle Social login request
    *
    * @return response
    */

   public function socialLogin($social)
   {
       return Socialite::driver($social)->redirect();
   }

   /**
    * Obtain the user information from Social Logged in.
    * @param $social
    * @return Response
    */

   public function handleProviderCallback($social)
   {
       $userSocial = Socialite::driver($social)->user();
       $user = User::where(['email' => $userSocial->getEmail()])->first();
       if($user){
           Auth::login($user);
           return redirect()->action('HomeController@index');
       }else{
           return view('auth.register',['name' => $userSocial->getName(), 'email' => $userSocial->getEmail()]);
       }
   }
}