I know. This line is unnecessary. If it cause bug, you can commit to delete it later but as I know right now. It didn't.

I will tell you if you don't know. Please look at https://github.com/composer/installers/blob/master/README.md#custom-install-paths.

You can use $type in custom path. That mean "css" in "type" will can put in custom path.
You can do something like.
```php
{
    "extra": {
        "installer-paths": {
            "assets/{$type}/{$name}/": ["twitter/boostrap"]
        }
    }
}
```