Route with optional param is not working

hello,
So I have routes like

PHP Code:

$route["admin/product/image/(:num)"]["delete"] = "product/deleteImage/$1"; 


so accessing
http://localhost/PROJECT/admin/product/image
as a delete request should work. But it leads to 404. I have to pass the last param to make it work.

any help is appreciated.

Harpreet Bhatia
Web Developer / Analyst
Technical Reviewer - "Codeigniter 2 Cookbook"