BM Controller returns 200 w/ empty body (jQuery 1.9 ) 

 http://jquery.com/upgrade-guide/1.9/#jquery-ajax-returning-a-json-result-of-an-empty-string

jQuery 1.9 ajax doesn't like 200's with empty bodies. a bit annoying but technically this is correct since it's not valid json. returning a 204 ( i.e. head :no_content )  instead corrects this.