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/Resource.js b/src/Resource.js
index f748fb5a..341193fa 100644
--- a/src/Resource.js
+++ b/src/Resource.js
@@ -128,7 +128,7 @@ ResourceFactory.prototype = {
         default:
           throw "Expected between 1-2 arguments [params, callback], got " + arguments.length + " arguments.";
         }
-        var data = isPostOrPut ? this : _undefined;
+        var data = isPostOrPut ? this : undefined;
         Resource[name].call(this, params, data, callback);
       };
     });