Running the migrator on pages that have a non-existent author will make the document listeners that check for the authorization behave unexpectedly.

In the context on the confluence migrator application, if some pages have been migrated, their authors will be confluence users that are not mapped in XWiki. Running the nested pages migrator on the imported pages will trigger various events, such as DocumentUpdatingEvent. If there is a listener for that specific event that checks for the authorization of the context user then the listener won't run as it should.

Since the nested pages migration is run manually by a user, the MoveAction executed for each page should implicitly have the author as the one running the migration.