protected function getSlugSource($from): string
    {
        if (is_null($from)) {
            return $this->model->__toString();
        }

        $sourceStrings = array_map(function($key) {
            $value = data_get($this->model, $key);
            if (is_bool($value)) {
                $value = (int) $value;
            }

            return $value;
        }, (array) $from);

        return implode($sourceStrings, ' ');
    }