Fix ConditionalRelease::Service rules_cache caching nil

Change-Id: Ib656a703867af79554e459a04bf4f0cba75f7fba
Reviewed-on: https://gerrit.instructure.com/90027
Tested-by: Jenkins
Reviewed-by: Dan Minkevitch <dan@instructure.com>
Product-Review: Dan Minkevitch <dan@instructure.com>
QA-Review: Dan Minkevitch <dan@instructure.com>

Author: Christian Prescott

app/models/conditional_release/service.rb

@@ -243,10 +243,8 @@ def rules_data(context, student, content_tags = [], session = {})
         end
       end
 
-      def rules_cache(context, student, force: false)
-        Rails.cache.fetch(rules_cache_key(context, student), force: force) do
-          yield if block_given?
-        end
+      def rules_cache(context, student, force: false, &block)
+        Rails.cache.fetch(rules_cache_key(context, student), force: force, &block)
       end
 
       def newer_than_cache?(items, cache)