NPE warnings related to "com.xpn.xwiki.doc.XWikiDocument.getAuthorReference" in DW logs when upgrading to XWiki 17.10.2

Steps to reproduce

1. Create an older instance of XWiki (tested with 11.10.13 and 12.6.8)
2. Start upgrading this instance to XWiki 17.10.2 by replacing the WAR
3. Observe the logs from the Distribution Wizard

Expected results

No warnings/ errors are displayed.

Actual results

The following warning is displayed under some documents:

Failed to get the Database List values. Root cause is [NullPointerException: Cannot invoke "com.xpn.xwiki.doc.XWikiDocument.getAuthorReference()" because the return value of "com.xpn.xwiki.objects.classes.DBListClass.getOwnerDocument()" is null]. 

The documents under which the stacktrace occurred are:

• XWiki > PDFExport > ConfigurationTemplate
• Image > Style > Code > ImageStyleTemplateProvider
• Help > Applications > Movies > Code > MoviesTemplateProvider

The issue seems to not be reproducing when upgrading to XWiki 17.4.8.