The value of Read only custom field cannot be cleared via PUT /rest/api/3/issue/{issueKeyOrId}

Issue Summary

The PUT /rest/api/3/issue/{issueKeyOrId} API allows to set the value of Read-Only Text Field, but once you pass empty string the value is not cleared.

Steps to Reproduce

1. Create a read-only custom field (ie. text cf)
2. Add your CF to screens in a project.
3. Set field value "some mistery value" via PUT /rest/api/3/issue/{issueKeyOrId}.
4. Set field value to "" via PUT /rest/api/3/issue/{issueKeyOrId}

Expected Results

The value is cleared (set to "none" or the request results in 400 with a proper error message, but I believe we should allow clearing the field value).

Actual Results

The value of the field remains unchanged. 

Workaround

Currently, there is no known workaround for this behavior. A workaround will be added here when available