Security level 'None' appears even when field is marked required

In select-list fields, JIRA automatically adds a 'None' option, unless the field is marked required. However with issue-level security, the 'None' option is always present. When the field is 'required' and None is selected, the form submission is guaranteed to fail, so it makes no sense and should be removed.

Workaround

Please refer the knowledge base article Remove NONE from the Issue Security Drop-Down List.