Hi Shimi and welcome to the Community. I am not familiar w/ the "Verifier" field. I'm guessing it may be associated w/ some QA addon you you or maybe it is just a custom field of type user-picker. If it is associated w/ an addon I would suggest reaching out to the addon's support. My experience w/ custom fields of type user-picker in Jira is that if you delete the current value (user) it should return to none/unassigned. I wonder if maybe that field lacks a default value.
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