This is related to #2841067: Exposed flag filter can't show unflagged nodes → when I set up a flag relationship I can also setup a "Flagged" filter. I can set it to not be required. All great. But I cannot set its default value to "". I can only set the default value to True or False. Other boolean filters like sticky allow an Any option when exposed:
Needs work
4.0
Views integration
The change is currently missing an automated test that fails when run with the original code, and succeeds when the bug has been fixed.
The patch will have to be re-rolled with new suggestions/changes described in the comments in the issue.
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