Merge pull request #1008 from braddunbar/missing-callback

`on` is a noop if no callback is provided

backbone.js

@@ -86,6 +86,7 @@
     // function. Passing `"all"` will bind the callback to all events fired.
     on: function(events, callback, context) {
       var ev;
+      if (!callback) return this;
       events = events.split(/\s+/);
       var calls = this._callbacks || (this._callbacks = {});
       while (ev = events.shift()) {

test/events.js

@@ -145,4 +145,8 @@ $(document).ready(function() {
     equal(counter, 2, 'unbind does not alter callback list');
   });
 
+  test("if no callback is provided, `on` is a noop", function() {
+    _.extend({}, Backbone.Events).bind('test').trigger('test');
+  });
+
 });