Clojure behavioral dispatch psuedo-code

psuedo_code.clj

(defprotocol ISpeak
  (hello [this]))

(defbehavior ::philip
  ISpeak
  (hello [_]
    (println "Hello, my name is Philip!")))

(defdispatch Person [this]
  [(:name this) (:age this)]) 

(defbehavior Person [::philip 26]
  ISpeak
  (hello [_]
    (println "Hello, my name is Philip! I'm 26.")))

(hello ::philip)
;; => Hello, my name is Philip!

(hello {:name ::philip :age 26})
;; => Hello, my name is Philip! I'm 26.

(hello nil)
;; => Uh-oh! What to do here? Maybe allow a :default key in defbehavior?