Lumen框架中无法解决的依赖项解析

Question

我有这样的错误

Fatal error: Uncaught Illuminate\Contracts\Container\BindingResolutionException: Unresolvable dependency resolving [Parameter #0 [ <required> string $name ]] in class Monolog\Logger in /laravel/vendor/illuminate/container/Container.php:994 

当我在UserController中调用操作创建时：

class UserController extends ApiController
{
private $userService;

/**
 * Create a new controller instance.
 *
 * @return void
 */
public function __construct(UserService $userService)
{
    $this->userService = $userService;
}

public function create(Request $request)
{
    $this->validate($request, [
        'first_name' => ['required', 'string'],
        'last_name' => ['required', 'string'],
        'email' => ['required', 'string', 'email', 'unique:users,email'],
        'permission_level' => ['required', 'int', 'in:' . implode(',', User::PERMISSION_LEVELS)],
    ]);

    /** @var User $user */
    $user = $this->userService->createUser($request->toArray());

    return response()->json($user->toArray());
}
}

我尝试使用命令php artisan cache:clear清除缓存，并将此行添加到 AppServiceProvider 类$this->app->singleton(UserService::class);中，但这无助于解决问题。