BillingController.getTransactions sporadically returns null items about androidbillinglibrary HOT 5 OPEN

private void updateOwnedItems() {
    if(Constants.LOGGING) Log.d(TAG,"updating owned items");
    List<Transaction> transactions = BillingController.getTransactions(this);
    //final ArrayList<String> ownedItems = new ArrayList<String>();
    if(Constants.LOGGING) Log.d(TAG,"transactions length="+transactions.size());
    for (Transaction t : transactions) {
        if(Constants.LOGGING) Log.d(TAG,"Evaluating Item="+t.productId);
        if (t.purchaseState == PurchaseState.PURCHASED) {
            //ownedItems.add(t.productId);
            if(t.productId.equals(RoundList.SYNC_SKU)) {
                if(Constants.LOGGING) Log.d(TAG,"found sync sku in owned items setting hasPurchasedSync=true");
                this.hasPurchasedSync=true;
            }
        }
    }
}