externs not being loaded?

gistfile1.txt

wei:routes wei$ ls
README.md	doc		externs		newrelic	out		project.clj	resources	src		target		test-data
wei:routes wei$ head -n 30 externs/google_maps_api_v3.js 
/*
 * Copyright 2010 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * @fileoverview Externs for the Google Maps v3 API.
 * @see http://code.google.com/apis/maps/documentation/javascript/reference.html
 * @externs
 */

google.maps = {};

/**
 * @enum {number|string}
 */
google.maps.Animation = {
  BOUNCE: '',
  DROP: ''

problem compiling

wei:routes wei$ lein cljsbuild clean; lein cljsbuild once prod
Deleting files generated by lein-cljsbuild.
Compiling ClojureScript.
Compiling "resources/public/javascript/client.js" from "src/cljs"...
WARNING: Protocol IPrintable is deprecated at line 18 /Users/wei/projects/clojure/routes/src/cljs/routes/color.cljs
WARNING: cljs.core/pr-sequential is deprecated. at line 18 /Users/wei/projects/clojure/routes/src/cljs/routes/color.cljs
WARNING: cljs.core/pr-sequential is deprecated. at line 18 /Users/wei/projects/clojure/routes/src/cljs/routes/color.cljs
WARNING: Protocol IPrintable is deprecated at line 158 src/cljs/routes/animation.cljs
WARNING: cljs.core/pr-sequential is deprecated. at line 158 src/cljs/routes/animation.cljs
WARNING: cljs.core/pr-sequential is deprecated. at line 158 src/cljs/routes/animation.cljs
WARNING: Protocol IPrintable is deprecated at line 18 src/cljs/routes/color.cljs
WARNING: cljs.core/pr-sequential is deprecated. at line 18 src/cljs/routes/color.cljs
WARNING: cljs.core/pr-sequential is deprecated. at line 18 src/cljs/routes/color.cljs
Oct 14, 2012 4:00:56 AM com.google.javascript.jscomp.LoggerErrorManager println
SEVERE: /Users/wei/projects/clojure/routes/.lein-cljsbuild-compiler-1/routes/client.js:11: ERROR - required "google.maps" namespace never provided
goog.require('google.maps');
^

ERROR: JSC_MISSING_PROVIDE_ERROR. required "google.maps" namespace never provided at /Users/wei/projects/clojure/routes/.lein-cljsbuild-compiler-1/routes/client.js line 11 : 0
Oct 14, 2012 4:00:56 AM com.google.javascript.jscomp.LoggerErrorManager println
SEVERE: /Users/wei/projects/clojure/routes/.lein-cljsbuild-compiler-1/routes/client.js:21: ERROR - required "google.maps.event" namespace never provided
goog.require('google.maps.event');
^

Oct 14, 2012 4:00:56 AM com.google.javascript.jscomp.LoggerErrorManager println
SEVERE: /Users/wei/projects/clojure/routes/.lein-cljsbuild-compiler-1/routes/yelp.js:6: ERROR - required "google.maps" namespace never provided
goog.require('google.maps');
^

Oct 14, 2012 4:00:56 AM com.google.javascript.jscomp.LoggerErrorManager printSummary
WARNING: 3 error(s), 0 warning(s)
ERROR: JSC_MISSING_PROVIDE_ERROR. required "google.maps.event" namespace never provided at /Users/wei/projects/clojure/routes/.lein-cljsbuild-compiler-1/routes/client.js line 21 : 0
ERROR: JSC_MISSING_PROVIDE_ERROR. required "google.maps" namespace never provided at /Users/wei/projects/clojure/routes/.lein-cljsbuild-compiler-1/routes/yelp.js line 6 : 0
Successfully compiled "resources/public/javascript/client.js" in 13.634981 seconds.

wei:routes wei$ wc -l resources/public/javascript/client.js
       0 resources/public/javascript/client.js

project.clj (snippet)

    :prod
    {:source-path "src/cljs"
     :compiler
     {:output-to "resources/public/javascript/client.js"
      :externs ["externs/google_maps_api_v3.js"]
      :optimizations :advanced
      :pretty-print true}}