remove _null and _undefined

they have no significant effect on minified and gziped size. in fact
they make things worse.

file        | before     | after removal
----------------------------------------
concat      | 325415     | 325297
min         | 62070      | 62161
min + gzip  | 25187      | 25176

The bottom line is that we are getting 0.05% decrease in size after
gzip without all of the hassle of using underscores everywhere.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/service/xhr.cache.js b/src/service/xhr.cache.js
index e87b127b..284321d7 100644
--- a/src/service/xhr.cache.js
+++ b/src/service/xhr.cache.js
@@ -26,7 +26,7 @@ angularServiceInject('$xhr.cache', function($xhr, $defer, $log){
   function cache(method, url, post, callback, verifyCache){
     if (isFunction(post)) {
       callback = post;
-      post = _null;
+      post = null;
     }
     if (method == 'GET') {
       var data, dataCached;