Meal Maker excercise

Hello everybody, this is my first post here: I’m really getting stuck with the Meal Maker excercise and I wish someone could help me understanding why.
I guess there’s a sintax error that I can’t find, related to the _courses object, since it gives me the following error
TypeError: Cannot read property ‘push’ of undefined
about line 37:

return this._courses[courseName].push(dish);
where I try to define the method for pushing a new dish into a specific course. I paste the entire code here below. Could someone help me understanding ? Thanks a lot
const menu = {
_courses: {
appetizers: ,
mains: ,
desserts:
},
get appetizers() {
return this._courses.appetizers;
},
get main() {
return this._courses.main;
},
get desserts() {
return this._courses.desserts;
},
set appetizers(appetizers) {
this._courses.appetizers = appetizers;
},
set main(mains) {
this._courses.main = mains;
},
set desserts(desserts) {
this._courses.desserts = desserts;
},
get courses() {
return {
appetizers: this.appetizers,
mains: this.mains,
desserts: this.desserts
};
},
addDishToCourse(courseName, dishName, dishPrice) {
const dish = {
name: dishName,
price: dishPrice,
};
return this._courses[courseName].push(dish);
},

getRandomDishFromCourse(courseName){
const dishes = this._courses[courseName];
const randomIndex = Math.floor(Math.random() * dishes.length);
return dishes[randomIndex];
},
generateRandomMeal(){
const appetizers = this.getRandomDishFromCourse(‘appetizers’);
const main = this.getRandomDishFromCourse(‘main’);
const desserts = this.getRandomDishFromCourse(‘desserts’);
const totalPrice = appetizer.price + main.price + desserts.price;
return Your meal is ${appetizer.name}, ${main.name}, ${desserts.name}. The price is ${totalPrice}.;
}
};

menu.addDishToCourse(‘appetizers’, ‘salad’, 4.25);
menu.addDishToCourse(‘appetizers’, ‘panini’, 5);
menu.addDishToCourse(‘appetizers’, ‘fries’, 3);
menu.addDishToCourse(‘main’, ‘maccheroni’, 4);
menu.addDishToCourse(‘main’, ‘riso cantonese’, 2);
menu.addDishToCourse(‘main’, ‘lasagne’, 8);
menu.addDishToCourse(‘desserts’, ‘tiramisu’, 3);
menu.addDishToCourse(‘desserts’, ‘yaourt’, 4);
menu.addDishToCourse(‘desserts’, ‘fruit’, 5);

const meal = menu.generateRandomMeal();
console.log(meal);

I am going to refer to this topic:

Learn Javascript Project Meal Maker - #2 by stetim94

Its seems like exactly the same issue

you’re right, thank you so much!