Billing address not provided

Dear All,

I am trying for 3 days now to work on checkout for guest on my site.

I am on NOPCOMMERCE V1.9

My Scenario is:
1. Guest Checkout allowd.
2. No Billing address for guest.
3. No shipping address as item dows not need to ship.
4. Payment method: Paypal Standard (I have set it up properly and working fine for registered user)

Now I have followed:
https://www.nopcommerce.com/boards/t/5200/can-i-remove-the-billing-address-step-from-the-wizard.aspx

Problem:
When I click on "Confirm" , it does not redirect me to paypal page. It is giving error message "Billing address not provided"

Other option already tried:
I have treid to comment out the total section

if (paymentInfo.BillingAddress == null)
                    {                      
                       throw new NopException("Billing address not provided");
                    }

Error: Object reference not set to an instance of an object.

Any help would be greatful.

Thanks.