protected function getAllowedTypeString($modelKey)
    {
        switch ($modelKey) {
            case 'addressable':
                return implode(",", array_keys(config('combine-core.validation.polymorphicTypes.addressable')));
            case 'author':
                return implode(",", array_keys(config('combine-core.validation.authorTypes')));
            case 'noteable':
                return implode(",", array_keys(config('combine-core.validation.polymorphicTypes.noteable')));
            case 'phoneable':
                return implode(",", array_keys(config('combine-core.validation.polymorphicTypes.phoneable')));
        };
        return null;
    }