array_key_exists expects parameter 2 to be array null given in CI3 Auth Class

Hi,

I've just updated a site to CI3 and am receiving the above error related to the following code snippet:

PHP Code:

// Get user from database
        $user = $CI->users->get(array("screen_name" => $attempt["screen_name"]));

        if (!array_key_exists("password", $user)) {
            return null;
        } 


This originally returned false but changed to null after reading the CI3 Upgrade Documentation. What would be the most optimal way to solve this error?