Only pass billing address details if they are present.

app/controllers/spree/checkout_controller_decorator.rb

@@ -390,6 +390,7 @@ module Spree
 
       # suggest current user's email or any email stored in the order
       opts[:email] = spree_current_user ? spree_current_user.email : order.email
+      if order.bill_address.present?
         opts[:address_override] = 1
         opts[:address] = {
           :name => order.bill_address.full_name,
@@ -401,7 +402,7 @@ module Spree
           :state => order.bill_address.state_text,
           :country => order.bill_address.country.iso
         }
-
+      end
       opts
     end