Meal maker project (Objects) cannot read property push but its supposed to be method?!

In the Meal Maker app I keep getting the same error.
In the 8th step. Which even in the video is supposed to be:

addDishToCourse(courseName, dishName, dishPrice){
const dish = {
name: dishName,
price: dishPrice
};
this._courses[courseName].push(dish)
},

I keep getting this error:
this._courses[courseName].push(dish)
^
TypeError: Cannot read property ‘push’ of undefined

But I am trying to push the const dish into the array (courseName) so (appetizers, main, desserts) which are array, why does it think that push is a property but not a method? I cant seem to find the mistake since its identical to the hint.

Did you look for existing topics first? I felt like I answered an identical question yesterday: