I'm not using ActiveSupport, so I don't have HashWithIndifferentAccess on a project. But I have a Gem that defines the module to add a method (specifically the mail gem) with this offending code:
Multibyte = Mail::Multibyte
I think a better check for this would be to check for HashWithIndifferentAccess itself.
Might be able to get a pull request sent for this, but I'm not sure how to approach the problem yet.