Investors and rental owners

There's another confusing issue, brought up in many other threads, such as this.

I have a T5 imported from CRA that Box 27 is empty, but Box 15 and 16 are USD (everything else is CAD). I edit the form, convert boxes 15 and 16 manually to CAD and enter the new numbers in TurboTax 15 and 16.
However I can't close the form now because it doesn't allow me to leave Source country of foreign income empty, although box 27, in the original statement, is empty, and it was imported empty.