Looking for feedback on my Meal Maker project

I just completed my Meal Maker project from the full stack developer skill path and I’m looking for feedback on my code regarding the efficiency/succinctness of my code and how to make it more efficient/succinct in the future. Thank you!!

const menu = { _courses: { appetizers: [], mains: [], desserts: [] }, get appetizers() { if (this._courses.appetizers != undefined || null) { return this._courses.appetizers; } else { return 'There are no appetizers available at the moment!' } }, get mains() { if (this._courses.mains != undefined || null) { return this._courses.mains; } else { return 'There are no mains available at the moment!' } }, get desserts() { if (this._courses.desserts != undefined || null) { return this._courses.desserts; } else { return 'There are no desserts available at the moment!' } }, set appetizers(newAppetizers){ if (typeof newAppetizers === 'string'){ this._courses.appetizers = newAppetizers } else { return 'Please input valid text.'; } }, set mains(newMains){ if (typeof newMains === 'string'){ this._courses.mains = newMains } else { return 'Please input valid text.'; } }, set desserts(newDesserts){ if (typeof newDesserts === 'string'){ this._courses.desserts = newDesserts } else { return 'Please input valid text.'; } }, get courses(){ if (this._courses != undefined || null) { return this._courses; } else { return 'No courses are available at the moment.' } }, addDishToCourse (courseName, dishName, dishPrice) { if (typeof courseName === 'string' && typeof dishName === 'string' && typeof dishPrice === 'number') { let dish = { dishName, dishPrice }; this._courses[courseName.toLowerCase()].push(dish); } else { return 'Please input valid values.'; } }, getRandomDishFromCourse (courseName) { if (typeof courseName === 'string') { let dishes = this._courses[courseName.toLowerCase()]; return dishes[Math.floor(Math.random()*dishes.length)] } }, generateRandomMeal () { const appetizer = this.getRandomDishFromCourse('appetizers') const main = this.getRandomDishFromCourse('mains') const dessert = this.getRandomDishFromCourse('desserts') const price = appetizer.dishPrice + main.dishPrice + dessert.dishPrice; return `For your appetizer you have ${appetizer.dishName}, with ${main.dishName} as the main course, and ${dessert.dishName} as a dessert to top it all off. Your total is ${price}.` } }; menu.addDishToCourse('mains', 'Chicken Wings', 5); menu.addDishToCourse('appetizers', 'Chicken Alfredo', 10); menu.addDishToCourse('desserts', 'Chocolate Mousse', 5); menu.addDishToCourse('mains', 'Chicken Tikka Masala', 5); menu.addDishToCourse('mains', 'Butter Chicken', 30); menu.addDishToCourse('appetizers', 'Butter Naan', 3); menu.addDishToCourse('appetizers', 'Garlic Naan', 3); menu.addDishToCourse('desserts', 'Tiramisu', 5); menu.addDishToCourse('desserts', 'Molten Lava Cake', 5); const meal = menu.generateRandomMeal(); console.log(meal);