How to get confirmTempUser to throw an error?

[seanpmaxwell]

For testing purposes I want to get

nev.confirmTempUser(req.params.URL, (err, user) => {
        
        if(err)
        {
            perror(err)
            res.status(404).json({ msg: 'confirm_temp_usr_failed' })
        }
        else if(user)
            res.render('index.html')
        else
            res.redirect('/bad-route')
    })

to throw an error. But if I do something like change the nev settings or turn off the internet, err is still null and it just returns the user as not found. How do I make the error not be null?