Mail notification with blank [//Target/AccountName]

I have a mail notification process that sends an email when a person moves out of set.

However, the move out also applies when the user is deleted, thus emails are sent that contain no data e.g. [//Target/AccountName] is blank.

Is there a built in way of validating that [//Target/AccountName] contains something, before getting to the Mail Notification Workflow activity? I considered that I could use an Authorization activity, but can't see how that would work.

I see the other alternatives being - to create a custom workflow activity (with an If Else condition) or to use something like the PowerShell workflow Activity.

Any advice gratefully received.

TIA,

Jon.