Pay's PaySubscription: what does `ends_at` mean?

I set up a yearly plan and subscribed to it with a test account. I was sort of expecting the `ends_at` of `PaySubscription` model to be a year from now, but it was blank.   Now, I know subscription plans auto-renew and so they don't have an `ends_at` ... but then what is `ends_at` for ?

If you pay for a month and cancel the next day, you should continue to have access until the end of the month you paid for.

The field tracks that end of period the user paid for when they cancel.

sounds like ends_at won't get set unless the subscriber cancels, and nil *is* the expected value for an active account?