Unable to use pmbootstrap flasher boot if pmbootstrap install hasn't been run

If the rootfs hasn't been generated, $ pmbootstrap flasher boot seems to fail:

$ pmb flasher boot
[18:30:50] ERROR: No kernel flavors installed in chroot 'rootfs_samsung-skomer'! Please let your device package depend on a package starting with 'linux-'.
[18:30:50] See also: <https://postmarketos.org/troubleshooting>

Run 'pmbootstrap log' for details.

Before you report this error, ensure that pmbootstrap is up to date.
Find the latest version here: https://gitlab.postmarketos.org/postmarketos/pmbootstrap/-/tags
Your version: 3.0.0_alpha

Pretty sure this wasn't the case before.