remove useless variable assignation

If the callback identifier is null or undefined, the 'getMapping' method already uses the 'DEFAULT' key - it is so useless to do this assignation before to call the method

script/Runner.js

diff --git a/script/Runner.js b/script/Runner.js
index 2c6218b..15789c5 100644
--- a/script/Runner.js
+++ b/script/Runner.js
@@ -159,10 +159,6 @@
     				if(i == undefined || i == null)
     				{
     					i = m.callbackId;
-        				if(i == undefined || i == null)
-        				{
-        					i = "DEFAULT";
-        				}
     				}
     				var callback = this.getMapping(i);
     				if(callback == undefined)