Upgrading exception from version 7 to 8.

[frogeyedman]

When upgrading the package from version 7 to 8 the following exception occurs (this only happens when the config file is cached).

vagrant@project:/vagrant$ composer install
> @php artisan package:discover --ansi

   Error

  Class name must be a valid object or a string

  at vendor/spatie/laravel-medialibrary/src/MediaLibraryServiceProvider.php:23
    19|         $this->registerPublishables();
    20|
    21|         $mediaClass = config('media-library.media_model');
    22|
  > 23|         $mediaClass::observe(new MediaObserver());
    24|
    25|         $this->loadViewsFrom(__DIR__.'/../resources/views', 'media-library');
    26|     }
    27|

      +8 vendor frames
  9   [internal]:0
      Illuminate\Foundation\Application::Illuminate\Foundation\{closure}()

      +5 vendor frames
  15  artisan:37
      Illuminate\Foundation\Console\Kernel::handle()

This happens because the config file is cached in the bootstrap/cache/config.php file, however php artisan config:clear cant be executed this will result in the following exception.

vagrant@project:/vagrant$ php artisan config:clear

   Error

  Class name must be a valid object or a string

  at vendor/spatie/laravel-medialibrary/src/MediaLibraryServiceProvider.php:23
    19|         $this->registerPublishables();
    20|
    21|         $mediaClass = config('media-library.media_model');
    22|
  > 23|         $mediaClass::observe(new MediaObserver());
    24|
    25|         $this->loadViewsFrom(__DIR__.'/../resources/views', 'media-library');
    26|     }
    27|

      +8 vendor frames
  9   [internal]:0
      Illuminate\Foundation\Application::Illuminate\Foundation\{closure}()

      +5 vendor frames
  15  artisan:37
      Illuminate\Foundation\Console\Kernel::handle()

This won't be a problem in a local environment because we do not cache the config file locally, but we do on production and test environments. The only solution (I am able to find) at the moment is to remove the bootstrap/cache/config.php file manually, will there be "easier" fix in the future ?

Many other people seem to have the same problem: https://github.com/spatie/laravel-medialibrary/issues?q=Class+name+must+be+a+valid+object+or+a+string