How to check if the Auto-renewable subscription active? Or: MKStoreKit's purchase record is always Null

Question

I need to implement In App Purchasing of Auto-renewable subscription in my app and using MKStoreKit v 6 for this purpose. The app successfully makes a purchase in a test account, but in property purchaseRecord I always have null against my product's ID. This is the output of purchaseRecord:

purchaseRecord: {
SKOrigBundleRef = "1.0";
"com.cName.aName.AutoSubscription" = "<null>";
}

Because of it, MKStoreKit's method expiryDateForProduct: always crashes.

Also, method isProductPurchased: always returns YES, independently whether the subscription active or expired.

How to check if the Auto-renewable Subscription expired or no using MKStoreKit or without it? In this case I can just write my own method to check it. I'll be very appriciate if you give an example code.

Thank you very much in advance!