Empty date column with workflow

This works with on-prem Nintex Workflow 2013

Problem:  Upon archiving a document I use workflow to update the date/time field of when the archive happened.  When user wants to un-archive the document, I need to clear the date field to display as empty (or null).

Resolution: 

1. Create variable vDateArchivedDate as Date and Time with blank default date
2. Use Convert value action input "1/1/0001" and store in variable vDateArchivedDate
3. Use Set field value to update the date column with workflow data > vDateArchivedDate