offboarding Journeys workflow notification need to include checklist owner name in subject line

Need help customizing the subject line for offboarding Journeys workflow notifications.

In our case, some of the payload attributes are returning null values. The requirement is to include only the checklist owner’s name in the subject line, without using any other payload attributes.

Please advise on the correct payload attribute or expression to use for displaying the checklist owner’s name in the notification subject?

Thanks in advance.