从5.2升级到Laravel 5.4后，我收到以下错误。我试过在很多论坛上搜索，但似乎没有人面临类似的问题。任何帮助都将受到高度赞赏。
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FatalThrowableError in ProviderRepository.php line 146:
Class 'Illuminate\Notifications\NotificationServiceProvider' not found
in ProviderRepository.php line 146
at ProviderRepository->createProvider('Illuminate\Notifications\NotificationServiceProvider') in ProviderRepository.php line 114
at ProviderRepository->compileManifest(array('Illuminate\Auth\AuthServiceProvider', 'Illuminate\Broadcasting\BroadcastServiceProvider', 'Illuminate\Bus\BusServiceProvider', 'Illuminate\Cache\CacheServiceProvider', 'Illuminate\Foundation\Providers\ConsoleSupportServiceProvider', 'Illuminate\Cookie\CookieServiceProvider', 'Illuminate\Database\DatabaseServiceProvider', 'Illuminate\Encryption\EncryptionServiceProvider', 'Illuminate\Filesystem\FilesystemServiceProvider', 'Illuminate\Foundation\Providers\FoundationServiceProvider', 'Illuminate\Hashing\HashServiceProvider', 'Illuminate\Mail\MailServiceProvider', 'Illuminate\Notifications\NotificationServiceProvider', 'Illuminate\Pagination\PaginationServiceProvider', 'Illuminate\Pipeline\PipelineServiceProvider', 'Illuminate\Queue\QueueServiceProvider', 'Illuminate\Redis\RedisServiceProvider', 'Illuminate\Auth\Passwords\PasswordResetServiceProvider', 'Illuminate\Session\SessionServiceProvider', 'Illuminate\Translation\TranslationServiceProvider', 'Illuminate\Validation\ValidationServiceProvider', 'Illuminate\View\ViewServiceProvider', 'App\Providers\AppServiceProvider', 'App\Providers\AuthServiceProvider', 'Illuminate\Broadcasting\BroadcastServiceProvider', 'App\Providers\EventServiceProvider', 'App\Providers\RouteServiceProvider', 'HieuLe\Active\ActiveServiceProvider', 'Anouar\Paypalpayment\PaypalpaymentServiceProvider', 'AdamWathan\BootForms\BootFormsServiceProvider', 'Laracasts\Flash\FlashServiceProvider', 'Webpatser\Countries\CountriesServiceProvider', 'Intervention\Image\ImageServiceProvider', 'Cviebrock\ImageValidator\ImageValidatorServiceProvider', 'Cmgmyr\Messenger\MessengerServiceProvider', 'Collective\Html\HtmlServiceProvider', 'App\Providers\CountNotificationProvider')) in ProviderRepository.php line 60
at ProviderRepository->load(array('Illuminate\Auth\AuthServiceProvider', 'Illuminate\Broadcasting\BroadcastServiceProvider', 'Illuminate\Bus\BusServiceProvider', 'Illuminate\Cache\CacheServiceProvider', 'Illuminate\Foundation\Providers\ConsoleSupportServiceProvider', 'Illuminate\Cookie\CookieServiceProvider', 'Illuminate\Database\DatabaseServiceProvider', 'Illuminate\Encryption\EncryptionServiceProvider', 'Illuminate\Filesystem\FilesystemServiceProvider', 'Illuminate\Foundation\Providers\FoundationServiceProvider', 'Illuminate\Hashing\HashServiceProvider', 'Illuminate\Mail\MailServiceProvider', 'Illuminate\Notifications\NotificationServiceProvider', 'Illuminate\Pagination\PaginationServiceProvider', 'Illuminate\Pipeline\PipelineServiceProvider', 'Illuminate\Queue\QueueServiceProvider', 'Illuminate\Redis\RedisServiceProvider', 'Illuminate\Auth\Passwords\PasswordResetServiceProvider', 'Illuminate\Session\SessionServiceProvider', 'Illuminate\Translation\TranslationServiceProvider', 'Illuminate\Validation\ValidationServiceProvider', 'Illuminate\View\ViewServiceProvider', 'App\Providers\AppServiceProvider', 'App\Providers\AuthServiceProvider', 'Illuminate\Broadcasting\BroadcastServiceProvider', 'App\Providers\EventServiceProvider', 'App\Providers\RouteServiceProvider', 'HieuLe\Active\ActiveServiceProvider', 'Anouar\Paypalpayment\PaypalpaymentServiceProvider', 'AdamWathan\BootForms\BootFormsServiceProvider', 'Laracasts\Flash\FlashServiceProvider', 'Webpatser\Countries\CountriesServiceProvider', 'Intervention\Image\ImageServiceProvider', 'Cviebrock\ImageValidator\ImageValidatorServiceProvider', 'Cmgmyr\Messenger\MessengerServiceProvider', 'Collective\Html\HtmlServiceProvider', 'App\Providers\CountNotificationProvider')) in Application.php line 530
at Application->registerConfiguredProviders() in RegisterProviders.php line 17
at RegisterProviders->bootstrap(object(Application)) in Application.php line 203
at Application->bootstrapWith(array('Illuminate\Foundation\Bootstrap\DetectEnvironment', 'Illuminate\Foundation\Bootstrap\LoadConfiguration', 'Illuminate\Foundation\Bootstrap\ConfigureLogging', 'Illuminate\Foundation\Bootstrap\HandleExceptions', 'Illuminate\Foundation\Bootstrap\RegisterFacades', 'Illuminate\Foundation\Bootstrap\RegisterProviders', 'Illuminate\Foundation\Bootstrap\BootProviders')) in Kernel.php line 232
at Kernel->bootstrap() in Kernel.php line 127
at Kernel->sendRequestThroughRouter(object(Request)) in Kernel.php line 99
at Kernel->handle(object(Request)) in index.php line 53