re-route with optional argument. possible bug??

hello there,
so i was working a project and tried to make an obvious route that did not work.
Example if you have a route like

PHP Code:

$route["admin/foos/(:num)"] = "admin/hello/$1"; 


and a function in admin controller as

PHP Code:

public function hello($arg=null) {
        if(empty($arg)){
            echo "is NULL";
        }
        else{
            echo "has $arg";
        }
    } 


1. The expected result on calling http://localhost/<project>admin/foos should be  (but is 404)

Code:

is NULL

2. calling url http://localhost/<project>/admin/foos/547 is as expected

Code:

has 547

Unexpectedly case 1 does not work, its lands to native CI 404 page. This only happens when you are making a route.
If I remove the route like

PHP Code:

// $route["admin/foos/(:num)"] = "admin/hello/$1"; 


and call url direclty  as http://localhost/<project>/admin/hello
the result is as expected

Code:

is NULL

http://localhost/<project>/admin/hello/586 is

PHP Code:

has 586 


The workaround i found was

PHP Code:

$route["admin/foos/?(:num)?"] = "admin/hello/$1"; 


Any help is appreciated.

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