Issues with custom redirect url using tokens when form field is empty

Question

I am trying to use Drupal webforms with tokens to build out a redirect url for my form submissions. Everything works great when all fields are populated, but if a field is left empty the redirect does not happen. Promo code is an optional field. This is with Webform 6.x-3.14

Redirect URL: %value[app_url]/user/new?email=%value[email_address]&first_name=%value[first_name]&last_name=%value[last_name]&promo_code=%value[promo_code]

Answer 1

I ended up writing a custom module to do the post using the following code as a starting point http://www.midwesternmac.com/blogs/jeff-geerling/integrate-webform-3x-paypal