Fix serializer

app/serializers/asciicast_serializer.rb

@@ -11,7 +11,7 @@ class AsciicastSerializer < ActiveModel::Serializer
     if v0_url?
       object.stdout_frames_url
     else
-      url = object.data.url
+      if url = object.data.url
         if url.starts_with?("/")
           asciicast_path(object, format: :json) # download URL for local carrierwave store
         else
@@ -19,6 +19,7 @@ class AsciicastSerializer < ActiveModel::Serializer
         end
       end
     end
+  end
 
   def private?
     object.private?