Laravel say that Auth guard [] is not defined

This could be a problem in your config/auth.php file, where the 'defaults' array is setting a non-existing guard on Laravel 5.2.

In case you edited your config/auth.php, e.g. to add another guard and your config is cached, your guards may not be reloaded. If you experience this problem, clearing the config will fix it.

$php artisan config:clear or $php artisan config:cache

I'm using laravel 5.5

Make sure that your config/auth.php is updated if you've upgraded from 5.1.x to 5.2.

https://github.com/laravel/laravel/blob/v5.2.0/config/auth.php