Migrating old Discussion Items failed in fact of a missing workflow state

[skillfully]

While in-place migration using the @@comment-migration view to migrate from plone v4.1.5 to v4.2.5 the process of migrating discussion items fails, because there is no workflow state for the old items and None is given

p.a.discussion 2.1.9 is installed

The instance was installed by the UnifiedInstaller.

Traceback (innermost last):

Module ZPublisher.Publish, line 126, in publish
Module ZPublisher.mapply, line 77, in mapply
Module ZPublisher.Publish, line 46, in call_object
Module plone.app.discussion.browser.migration, line 205, in __call__
Module plone.app.discussion.browser.migration, line 124, in migrate_replies
AttributeError: 'NoneType' object has no attribute 'get'