코드 배포 관련 에러가 무슨에러인지 모르겠습니다

syntax error, unexpected '?' /home/deployer/www/releases/release_20180628085949/vendor/symfony/http-foundation/Response.php #0 /home/deployer/www/releases/release_20180628085949/vendor/composer/ClassLoader.php(322): Composer\Autoload\includeFile('/home/deployer/...') #1 [internal function]: Composer\Autoload\ClassLoader->loadClass('Symfony\\Compone...') #2 /home/deployer/www/releases/release_20180628085949/vendor/laravel/framework/src/Illuminate/Http/Response.php(13): spl_autoload_call('Symfony\\Compone...') #3 /home/deployer/www/releases/release_20180628085949/vendor/composer/ClassLoader.php(444): include('/home/deployer/...') #4 /home/deployer/www/releases/release_20180628085949/vendor/composer/ClassLoader.php(322): Composer\Autoload\includeFile('/home/deployer/...') #5 [internal function]: Composer\Autoload\ClassLoader->loadClass('Illuminate\\Http...') #6 /home/deployer/www/releases/release_20180628085949/vendor/laravel/framework/src/Illuminate/Routing/ResponseFactory.php(55): spl_autoload_call('Illuminate\\Http...') #7 /home/deployer/www/releases/release_20180628085949/vendor/laravel/framework/src/Illuminate/Foundation/helpers.php(795): Illuminate\Routing\ResponseFactory->make(Object(Illuminate\View\View), 400, Array) #8 /home/deployer/www/releases/release_20180628085949/app/Exceptions/Handler.php(64): response(Object(Illuminate\View\View), 400) #9 /home/deployer/www/releases/release_20180628085949/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(326): App\Exceptions\Handler->render(Object(Illuminate\Http\Request), Object(Symfony\Component\Debug\Exception\FatalThrowableError)) #10 /home/deployer/www/releases/release_20180628085949/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(124): Illuminate\Foundation\Http\Kernel->renderException(Object(Illuminate\Http\Request), Object(Symfony\Component\Debug\Exception\FatalThrowableError)) #11 /home/deployer/www/releases/release_20180628085949/public/index.php(55): Illuminate\Foundation\Http\Kernel->handle(Object(Illuminate\Http\Request)) #12 {main} Exception thrown without a stack frame Unknown #0 /home/deployer/www/releases/release_20180628085949/vendor/laravel/framework/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(137): Symfony\Component\Debug\Exception\FatalErrorException->__construct() #1 /home/deployer/www/releases/release_20180628085949/vendor/laravel/framework/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(123): Illuminate\Foundation\Bootstrap\HandleExceptions->fatalExceptionFromError() #2 /home/deployer/www/releases/release_20180628085949/vendor/laravel/framework/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(0): Illuminate\Foundation\Bootstrap\HandleExceptions->handleShutdown() #3 {main} public dns를 입력하면 slack으로 위와 같은 로그가 옵니다. HTTP ERROR 500 에러코드를 가지고있습니다.