Multimethod Not Working

multimethod.clj

;; Trying to use type hinting to differentiate between two single-arg methods,
;; but I suspect I'm doing it totally wrong

(defmulti add-vertex (fn [& args] (map class args)))
(defmethod add-vertex [] (add-vertex nil nil))
(defmethod add-vertex Integer [id] (add-vertex id nil))
(defmethod add-vertex Map [props] (add-vertex nil props))
(defmethod add-vertex [Integer Map] [id props]
  ((let [vertex (. *g* addVertex id)]
     (when props
       (apply set-property! vertex (interleave (map name (keys props)) (vals props))))
     vertex)))