Delivery Note status is on 'To Bill' even if the amount is zero

I made a Saler Order with a product which has the rate in $0.00. I made the Delivery Note based on that Sales Order but the amount is zero. When I does that, the status changed “to Bill”. Does I have to made a Sales Invoice for the status to change to “Completed” even if the amount is zero?.

If you do:
Sales Order > Delivery Note
And then back to
Sales Order > Sales Invoice, status at Delivery Note will keep as “To bill”.

To solve it you must do:
Sales Order > Delivery Note > Sales Invoice

I just raised an issue at github: