FileCollection and addDirectory

Hello,
I was trying to use the FileCollection class that is documented at https://codeigniter.com/user_guide/libra...ollections but I can't get it to work and I don't know if the problem is me or the documentation
I just did something stupid like this in a class that extends a BaseCommand.

PHP Code:

$Scripts = new \CodeIgniter\HTTP\Files\FileCollection([]);
 $Scripts->addDirectory(APPPATH.'Database/sqlUpdates');
$Scripts->retainPattern('*.sql');
CLI::write(count($Scripts)." found in the App/Database/sqlUpdates folder"); 


Nothing too fancy. and pretty similar to the example given.
Running this I get:

Code:

Call to undefined method CodeIgniter\HTTP\Files\FileCollection::addDirectory()

which frankly seems reasonable since I have nothing called "addDirectory" (neither retainPattern) in my entire source tree.

I feel like I'm missing something obvious, can someone give me an hint?

Thanks.