I am wanting to upgrade from 3.0-alpha4 to 4.0-beta2.
After upgrading and running the database update "8001 - Provide upgrade path from 8.x-3.x to 8.x-4.x." the view is now non functional (crashing the site).
The issue is due to the use of bef_ul (nested checkboxes) in 3.0-alpha4 which is no longer present in 4.0-beta.
After manually updating my configuration yml from bef_ul to bef, everything was once again functional.
1. use 3.0-alpha4
2. add nested checkbox exposed filter
3. upgrade to 4.0-beta2
4. run database update
5. open the view, you will have an error
6. export config
7. change bef_ul to bef
8. import config
9. open the view, should be functional again
Adjust the migration to correctly migrate bef_ul to bef.
Closed: cannot reproduce
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
So not seeing bef_ul in 6.0.x, believe this ticket is outdated. Just became a co-maintainer so helping clean up the issue queue but if still a valid bug in 6.0.x please reopen.