(prxml-data []) --> What gives?

dispatcher-test.clj

(defn dispatcher
  [node]
  (condp = (class node)
    clojure.lang.PersistentVector   ::vector
    clojure.lang.PersistentArrayMap ::map
    clojure.lang.PersistentList     ::sequence
    java.lang.Integer               ::atomic
    java.lang.String                ::atomic))

(defmulti prxml-data
  "Make a data structure that can be consumed by clojure.contrib.prxml/prxml"
  dispatcher)

(defmethod prxml-data ::vector
  [node & parent-name]
  [parent-name
   (reduce vec (for [n node]
                 (prxml-data n node)))])

(defmethod prxml-data ::map
  [node & parent-name]
  (for [k (keys node)]
    [k (prxml-data (k node))]))

(defmethod prxml-data ::sequence
  [s & parent-name]
  [parent-name (reduce concat (dbg (for [n s]
                 (prxml-data n))))])

(defmethod prxml-data ::atomic [n] n)

user=> (prxml-data [])
java.lang.IllegalArgumentException: No matching clause: clojure.core$class@4891d863 (NO_SOURCE_FILE:0)

What gives?