Script @php artisan package:discover handling the post-autoload-dump event returned with error code 255

This is how I solved this after an upgrade from laravel version 6.x – 7.x:

In App\Exceptions\Handler changed

//Use Exception;
Use Throwable;

Then methods to accept instances of Throwable instead of Exceptions as follows:

//public function report(Exception$exception);
public function report(Throwable $exception);

//public function render($request, Exception $exception);
public function render($request, Throwable $exception);

In config\session.php:

//'secure' => env('SESSION_SECURE_COOKIE', false),
'secure' => env('SESSION_SECURE_COOKIE', null),

Then run composer update