Erro ao converter valor de variavel

Ocorre um erro quando tendo converter o valor da variável happiness de 'String' para 'Int'.

Erro: Value of optional type 'String?' not unwrapped; did you mean to use '!' or '?'?

segue o código.

import UIKit

class ViewController: UIViewController {

    @IBOutlet var nameField: UITextField?
    @IBOutlet var happinessField: UITextField?

    @IBAction func add(){
        if nameField == nil || happinessField == nil {
            return
        }

        let name = nameField!.text
        let happiness = happinessField!.text.toInt()

        if happiness == nil {
            return
        }

        let meal = Meal(name: name, happiness: happiness!)

        println("eaten: \(meal.name) \(meal.happiness)")
    }
}