As per the [documentation](https://php-etl.gitbook.io/docs/extractors/collection), the source in `$etl->extrac` can also be an iterable: `$etl->extract('collection', $iterable, $options);` When I do that phpstan complains about the [type in your code](https://github.com/leomarquine/php-etl/blob/master/src/Etl.php#L53).