This was reported as an issue in the twitter gem. Upon investigation, it appears to be a bug in the Twitter API.
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When was the old resource deprecated? Were there any other resources that changed at the same time? I try to pay close attention to the Twitter API Announcements list, but don't recall seeing anything about this. Could you direct me to the relevant post?
I'm disappointed that the documentation is not keeping up with the API. If anything, the documentation should be coming ahead of changes, not trailing them.