Gold Challenge - was my build supposed to fail?

I added this failable initializer in my Monster class, but no errors appeared when I built it pointing to my Zombie subclass, which the challenge suggests I’d need to adjust:

 // gold challenge
    // failable initializer
    init?(town: Town?, monsterName: String?) {
        guard monsterName != nil else {
            return nil
        } = town = monsterName ?? "\(String(describing: town?.numberOfStoplights)) Spotlights Monster"

Is there something wrong with my failable initializer?