Easily reproducible, not so easily explainable:
- Argument 1 passed to array_fuse() must be of the type array, boolean given, called in /core/lib/phabricator/src/applications/search/field/PhabricatorSearchCheckboxesField.php on line 26 and defined
I've attempted to work out what combination of form settings results in this query hash, unfortunately without success. I can't seem to reproduce it with the form, however, this seems like like a valid bug with an easy fix. I'll submit a diff.