title: InAppBilling V3 - "purchaseData" and "dataSignature" are null when purchasing subscription item
body: <p>I have a problem purchasing subsciption items with the new InAppBilling V3</p>
  
  <p>Here's my IABHelper's handleActivityResult method:</p>
  
  <pre><code>    public boolean handleActivityResult(int requestCode, int resultCode, Intent data) {
              IabResult result;
              if (requestCode != mRequestCode)
                  return false;
  
              checkSetupDone("handleActivityResult");
  
              // end of async purchase operation
              flagEndAsync();
  
              if (data == null) {
                  Log.e(TAG + "Null data in IAB activity result.");
                  result = new IabResult(IABHELPER_BAD_RESPONSE, "Null data in IAB result");
                  if (mPurchaseListener != null)
                      mPurchaseListener.onIabPurchaseFinished(result, null);
                  return true;
              }
  
              int responseCode = getResponseCodeFromIntent(data);
              String purchaseData = data.getStringExtra(RESPONSE_INAPP_PURCHASE_DATA);
              String dataSignature = data.getStringExtra(RESPONSE_INAPP_SIGNATURE);\
              ...
  </code></pre>
  
  <p>purchaseData and dataSignature are null after that code, and as a result, the purchase flow can't be completed.</p>
  
  <p>When Im trying to purchase in-app items, all works well. purchaseData and dataSignature aren't null.</p>
  
  <p>This guy seem to had the same problem:<br>
  <a href="https://stackoverflow.com/questions/16377755/google-play-in-app-purchase-returns-error-code-1008-null-puchasedata-or-datasi">Google Play In-App Purchase returns error code -1008: null puchaseData or dataSignature</a></p>
  
  <p>but it doesn't work for me, Im still getting null for the both fields.</p>
  
  <p>What am I doing wrong? thanks in advance!</p>