如果控制器方法中缺少参数，如何重定向？

Suppose I am creating a dynamic file and I will pass variable inside method_name($variable) and $variable having name ("abc") then our path look like for example:

http://localhost/folder_name/index.php/controller_name/method_name/abc

If I remove abc from the following path then url will look like http://localhost/folder_name/index.php/controller_name/method_name/

and then we run on browser then it will show error i.e.

Message: Missing argument 1 for method_name::controller_name().

So, My question is how to redirect a file if variable value is remove from method. I want to redirect a file to controller if method having nothing inside it.

Thank You

Just Check argument

<?php
class Blog extends CI_Controller {

    public function index($abc = NULL)
    {
         if($abc){
            // IF argument 
            echo 'Hello World!';
         }else{
            // Redirect here if not argument parsed
         }
    }
}