Phone Call Activity Default Notification Is Blank When DONOTPHONE = True On Contact

We are using CRM 2016 v8.1 onPrem. We recently noticed that if a contact has DONOTPHONE = true, then when a user creates a phone call activity, then when the activity is saved, there is a BLANK error notification on the phone activity. How can I clear this OOTB notification? Or can I can add a custom message to the OOTB notification since this is blank?  I know how to add a custom notification but I need to get rid of this one.

Thanks in advance,

Chrys