I'm getting the error "An unhandled exception occurred during the execution of the workflow instance. Exception details: System.ArgumentNullException: Value cannot be null." when attempting to run the below workflow in a SharePoint Online Add-In:
To troubleshoot the issue, check things below:
Debug the workflow to check if you can get list item and create the list item in another list. Make sure there is value in the required field when creating item in another list.
Restart the workflow again and check result.
Error "An unhandled exception occurred ... Value cannot be null".
Add a workflow to a SharePoint-hosted SharePoint Add-in.