Multi-Authentication Error

I'm following a tutorial on how to add multiple authentication systems to a Laravel 10 app using Jetstream package. A login system for users and a separate one for admins. The tutorial is using Laravel 9 and despite following everything step by step, I'm getting the error below when I navigate to admin/login route: Kindly follow this link to download a sample app that I'm working on. Please remember to create an auth_app database first, then run your migration and finally, you run the app.

App\Http\Controllers\AdminController::__construct(): Argument #1 ($guard) must be of type Illuminate\Contracts\Auth\StatefulGuard, null given

This is the class that is throwing the exception:

use Illuminate\Http\Request;
use Laravel\Fortify\Fortify;
use Laravel\Fortify\Features;
use Illuminate\Routing\Pipeline;
use Illuminate\Routing\Controller;
use App\Http\Responses\LoginResponse;
use Illuminate\Contracts\Auth\StatefulGuard;
//use Laravel\Fortify\Contracts\LoginResponse;
use Laravel\Fortify\Contracts\LogoutResponse;
use Laravel\Fortify\Http\Requests\LoginRequest;
use Laravel\Fortify\Contracts\LoginViewResponse;
use App\Actions\Fortify\AttemptToAuthenticate;
use Laravel\Fortify\Actions\EnsureLoginIsNotThrottled;
use Laravel\Fortify\Actions\PrepareAuthenticatedSession;
use App\Actions\Fortify\RedirectIfTwoFactorAuthenticatable;

class AdminController extends Controller
{
    /**
     * The guard implementation.
     *
     * @var \Illuminate\Contracts\Auth\StatefulGuard
     */
    protected $guard;

    /**
     * Create a new controller instance.
     *
     * @param  \Illuminate\Contracts\Auth\StatefulGuard  $guard
     * @return void
     */
    public function __construct(StatefulGuard $guard)
    {
        $this->guard = $guard;
    }

    public function login()
    {
        //return view('auth.login', ['guard' => 'admin']);
        return view('auth.login', ['guard' => $this->guard?->name]);
    }

    /**
     * Show the login view.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return \Laravel\Fortify\Contracts\LoginViewResponse
     */
    public function create(Request $request): LoginViewResponse
    {
        return app(LoginViewResponse::class);
    }

    /**
     * Attempt to authenticate a new session.
     *
     * @param  \Laravel\Fortify\Http\Requests\LoginRequest  $request
     * @return mixed
     */
    public function store(LoginRequest $request)
    {
        return $this->loginPipeline($request)->then(function ($request) {
            return app(LoginResponse::class);
        });
    }

    /**
     * Get the authentication pipeline instance.
     *
     * @param  \Laravel\Fortify\Http\Requests\LoginRequest  $request
     * @return \Illuminate\Pipeline\Pipeline
     */
    protected function loginPipeline(LoginRequest $request)
    {
        if (Fortify::$authenticateThroughCallback) {
            return (new Pipeline(app()))->send($request)->through(array_filter(
                call_user_func(Fortify::$authenticateThroughCallback, $request)
            ));
        }

        if (is_array(config('fortify.pipelines.login'))) {
            return (new Pipeline(app()))->send($request)->through(array_filter(
                config('fortify.pipelines.login')
            ));
        }

        return (new Pipeline(app()))->send($request)->through(array_filter([
            config('fortify.limiters.login') ? null : EnsureLoginIsNotThrottled::class,
            Features::enabled(Features::twoFactorAuthentication()) ? RedirectIfTwoFactorAuthenticatable::class : null,
            AttemptToAuthenticate::class,
            PrepareAuthenticatedSession::class,
        ]));
    }

    /**
     * Destroy an authenticated session.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return \Laravel\Fortify\Contracts\LogoutResponse
     */
    public function destroy(Request $request): LogoutResponse
    {
        $this->guard->logout();

        $request->session()->invalidate();

        $request->session()->regenerateToken();

        return app(LogoutResponse::class);
    }
}