Test rails 4.1 beta
When the facet parameter (f) is blank, remove it.
Don't use complex objects (e.g. HashWithIndifferentAccess) in session
In rails 4.1 the default session serializer has been switched to a JSON
serializer, which doesn't support serializing class.

See https://github.com/rails/rails/pull/13945#issuecomment-34090370