In app billing API v3 INAPP_PURCHASE_DATA is null

In app billing API v3 INAPP_PURCHASE_DATA is null

I am implementing subscription billing using the Version 3 Billing API.
After the payment dialog has closed (payment succeeded), control is
returned back to my activity
@Override
protected void onActivityResult(int requestCode, int resultCode,
Intent data) {
if (resultCode == Activity.RESULT_OK) {
// Null
String purchaseData = data.getStringExtra("INAPP_PURCHASE_DATA"
}
}
The problem is that the purchaseData string is null. This might be because
I have already purchased this subscription ( a million times when testing
) - and that I should have checked with getPurchases() first.
Is it known for purchases to "go through - apparently with success", if
the user tries to pay when he or she is 1) a current subscriber, or 2) in
the period after cancelleation but before the service expires?