Fatal error: Default value for parameters with a class type hint can only be NULL in hook_user_presave()

I get this when enabling Pants module after running drush dmu-upgrade on it.

The line in question is:

function pants_user_presave(\Drupal\user\UserInterface $edit = [], \Drupal\user\UserInterface $account = [], \Drupal\user\UserInterface $category = []) {

Also, above that there are not 1, not 2... not even 3! But *6* instances of this:

 * @FIXME
 * The $edit and $category parameters are gone in Drupal 8. They have been left
 * here in order to prevent 'undefined variable' errors, but they will never
 * actually be passed to this hook. You'll need to modify this function and
 * remove every reference to them.

Well as long as we're thorough. :D