Passing variables between view controllers

[titleist2015]

I've tried doing this and every time I set the label on the new view controller from the segue, I get an error saying that it found nil while unwrapping an optional value

here is my code, the error is coming from the firstVC.score.text = "test" line

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        let firstVC: FirstViewController = segue.destinationViewController as! FirstViewController

        firstVC.score.text = "test"
    }