Allow `time` field to be empty

We have a case where we need to have an optional field of type time. For some reason, frappe won’t allow the field to be blank. While saving a doc, the field always defaults to the current time if empty.

Is there a way to prevent this?

My Frappe verison:
Frappe Framework: v14.38.0 (HEAD)

If it looks like a bug, we can raise a git issue for the same…