Error in Defining new Exercise (4.7)

[abdollahkahne]

Because push is only defined for array. when I want to add a video for new exercise it doesnt work and doesnt add ng-form to view.
I corrected it in the model for Exercise Construc function as below:

if (!args.videos) {
                this.related.videos=[];//we should specify type of videos as arrays!
            }

But I am sure there is better way for this. Any suggestion?!
Thanks