Problem/Motivation
I am migrating wimleers.com from D7 to D8. It contains comments from the D5/D6 days. It looks like this:
Note that the language column is empty ('') for the upper half of the rows displayed, but set to the unspecified language code ('und') for the bottom half. The upper half are comments upgraded from D5/D6. The bottom half are comments created in D7.
When migrating comments with entity validation turned on (see #2745797: Add option to content entity destinations for validation and #3095456: [Plan] Discuss strategy for long term use of entity validation in the migration system), this causes lots of validation errors:
Proposed resolution
Detect this edge case in \Drupal\comment\Plugin\migrate\source\d7\Comment and automatically fix it.
Remaining tasks
None.
User interface changes
None.
API changes
None.
Data model changes
None.
Release notes snippet
TBD