Revise a Time Sheet to have it be zero hours

On occasion, our users have had need to revise a billable time sheet to remove Billable hours to a project. We use classic time entry.

This happens when there is only one line on the time report and one project.

We have tried to have them do a revision leaving the project but blanking out the hours, thinking that this would allow a "revision" to flow through to the proj resource table.  When you click 'submit' it clears out the project and makes it a zero line row and you receive an email stating "Time Adjustment could not be submitted due to system error. Please contact your system administrator."