Err "missing form body" on POST request when the body is nil

[akoserwal]

http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		r.Body = nil
		store, err := sessionManager.Start(context.Background(), w, r)
		if err != nil {
			fmt.Fprint(w, err)
			return
		}
}

Err:"missing form body"