如何在Golang中使用MUX路由器路径？

Using github.com/gorilla/mux I do this:

router := mux.NewRouter().StrictSlash(true)
    router.HandleFunc("/qa/{cat}",qaall)
        router.HandleFunc("/qadetail/{id}",GetQuestionAnswerDetail) 

Above file is working because we pass the {} but when we pass this on

router.HandleFunc("/AddQuestion",AddQuestion)

It gives me the following error:

http: panic serving 127.0.0.1:57748: ObjectIDs must be exactly 12 bytes long (got 0)