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If we use REST via the API console to delete a group, I get
"description": "The request body is either missing or incomplete",
"debug": "Request came in with a missing body"
However, there is no place, on a delete, on that API console, for us to provide a body, even a blank one.
Additionally, http://devcenter.kinvey.com/rest/guides/users#usergroups the update example seems not be documented correctly (looks like a bug in how you auto-generate your docs)