Email "" does not comply with addr-spec of RFC 2822

The notification sometimes returns a null value, I know this is not expected, but it does happen sometimes in my actual scenario.
For example, if the approver's role is set up, when the approver leaves the job at a certain time, there is no new approver to replace him.
At this point in our project his work will be taken over by the super administrator.
But the approver's notification settings will not be updated because this will only last for a short period of time.
But you will encounter this problem here, the notification actually has no recipients.