The Monster class can be initialized with any String instance for the monsterName parameter, even an empty String. Doing so would lead to an instance of Monster with no name. Even though Frankenstein’s monster had no name, you want all of yours to be individually identified. Fix this problem in the Monster class by ensuring that monsterName cannot be empty.
Your solution will involve giving Monster a failable initializer. Also note that this change will have an impact on initialization in the Zombie subclass. Make the necessary adjustments in this class as well.