$session->destroy() throws exception

You are assigning variables to session variables that may not exist. If that session variable does not exist you will get an exception.  If you are running Codeigniter in development mode, the displayed webpage would likely highlight the problem line of code.

Not sure I understand what you mean.

$session->get() will not throw an exception if the requested key name does not exist, it will simply return "nothing".

The exception points to $session->destroy(), as I outlined above.

-joho