php artisan doesn't work [ErrorException] Undefined offset: 0 in Laravel 5.1

public function offsetGet($key)

{

   //here

    return $this->items[$key];

}

https://laracasts.com/discuss/channels/laravel/php-artisan-doesnt-work-errorexception-undefined-offset-0-in-laravel-51?page=0

via Chebli Mohamed