ReflectionClass error. in Upgrading laravel 5.1 to 5.8

I am following https://medium.com/@info.subashthapa/upgrading-laravel-5-0-to-5-8-1bfec5c8a0e2

to upgrade laravel 5.1 to laravel 5.8 now I have stuck in that error

PHP Fatal error:  Uncaught ReflectionException: Class App\Console\Kernel does not exist in D:\xampp\htdocs\cloud\vendor\laravel\framework\src\Illuminate\Container\Container.php:741
Stack trace:
#0 D:\xampp\htdocs\cloud\vendor\laravel\framework\src\Illuminate\Container\Container.php(741): ReflectionClass->__construct('App\\Console\\Ker...')
#1 D:\xampp\htdocs\cloud\vendor\laravel\framework\src\Illuminate\Container\Container.php(631): Illuminate\Container\Container->build('App\\Console\\Ker...', Array)
#2 D:\xampp\htdocs\cloud\vendor\laravel\framework\src\Illuminate\Foundation\Application.php(674): Illuminate\Container\Container->make('App\\Console\\Ker...', Array)
#3 D:\xampp\htdocs\cloud\vendor\laravel\framework\src\Illuminate\Container\Container.php(220): Illuminate\Foundation\Application->make('App\\Console\\Ker...', Array)
#4 D:\xampp\htdocs\cloud\vendor\laravel\framework\src\Illuminate\Container\Container.php(738): Illuminate\Container\Container->Illuminate\Container\{closure}(Object(Illuminat in D:\xampp\htdocs\cloud\vendor\laravel\framework\src\Illuminate\Container\Container.php on line 741

I have found out ReflectionClass; in fresh laravel 5.8 but I didn't get.

I download composer.json from server I surprised its file got invalid json. I don't know how it happens.

I tried copy composer.json to replace old composer.json still I got error ReflectionClass error.

Please Suggest me.

via Chebli Mohamed