Right now it's possible to select an action without specifying any parameter. Specifically, this is possible for "throttle" (just leave the fields blank), "warn" (select "other message" and leave the field blank) and "tag" (blank field) options. I think those fields should be required and validated server-side as well, if their checkbox is selected.
My proposal is to wait for OOUI conversion (T132284), then add the needed validation. In fact, with OOUI some field types will be changed and would require a brand new validation system.
Another thing is to avoid validation for hidden fields, see T203336#4551702.
- Throttle field
- Warn field
- Disallow field
- Tag field
- No validation for hidden fields