Fix subscription creation. Coupon.max_redemptions is optional and can be nil

Author: rydama

lib/stripe_mock/request_handlers/subscriptions.rb

@@ -63,7 +63,7 @@ def create_customer_subscription(route, method_url, params, headers)
           coupon = coupons[coupon_id]
 
           if coupon
-            if coupon[:times_redeemed] >= coupon[:max_redemptions]
+            if coupon[:max_redemptions].present? && coupon[:times_redeemed] >= coupon[:max_redemptions]
               raise Stripe::InvalidRequestError.new("Coupon #{coupon[:id]} is used up and cannot be applied.", 'coupon', http_status: 400)
             end
 
@@ -134,7 +134,7 @@ def create_subscription(route, method_url, params, headers)
           coupon = coupons[coupon_id]
 
           if coupon
-            if coupon[:times_redeemed] >= coupon[:max_redemptions]
+            if coupon[:max_redemptions].present? && coupon[:times_redeemed] >= coupon[:max_redemptions]
               raise Stripe::InvalidRequestError.new("Coupon #{coupon[:id]} is used up and cannot be applied.", 'coupon', http_status: 400)
             end
 
@@ -245,7 +245,7 @@ def update_subscription(route, method_url, params, headers)
 
           coupon = coupons[coupon_id]
           if coupon
-            if coupon[:times_redeemed] >= coupon[:max_redemptions]
+            if coupon[:max_redemptions].present? && coupon[:times_redeemed] >= coupon[:max_redemptions]
               raise Stripe::InvalidRequestError.new("Coupon #{coupon[:id]} is used up and cannot be applied.", 'coupon', http_status: 400)
             end