fixes #857. All the generics now ignores the call of the method if th…

…e passed element is null or undefined. #each now doesnt iterate the windows if you pass null or undefined as the iterable.

Source/Core/Core.js

@@ -166,6 +166,7 @@ var implement = function(name, method){
 	if (previous == null || !previous.$protected) this.prototype[name] = method;
 
 	if (this[name] == null && typeOf(method) == 'function') extend.call(this, name, function(item){
+		if (item == null) return;
 		return method.apply(item, Array.prototype.slice.call(arguments, 1));
 	});