Avoid Errors due to missing ID in URL header

Using Codeigniter + Bonfire framework I can pass variables in my URL. This all works great with GET function like so:

in my view file I get ID of my user and on click pass it to controller again:

<a href="/my_team/index/<?php echo $user->member->id; ?>">Something</a>

controller then receives ID:

public function index($id = null) {

    //do stuff with that id...
}

URL looks like this:

http://mysite/my_team/index/26

And everything on that page knows user has ID of 26 and display information correctly.

Problem is if I manually remove that number from the URL so it looks like this:

http://mysite/my_team/index/

and leave the index in the URL I now get a whole bunch of errors because the site can't get the ID from URL. How can I avoid this? Maybe hide the index public function from the URL using .htacces or something?

Like @CBroe said in his comment. Something like this:

public function index($id = null) {

   if(is_null($id)) {
      // redirect to custom error page
   }

    //do stuff with that id...
}