Angular 6 Material Design dialogs and validation

I’m not sure if this is the right place or not.
I’m trying to use Angular 6, Material Design Dialogs and get validation to work within the dialog.
I created an example of what I’m doing in plunker, but there’s an error on plunker and I’m not sure what’s wrong there. I don’t get that error on my machine, so it’s something I don’t have right on plunker.

my app works, except that in the dialog, it shows when I don’t have a required field filled in, but the OK button will still be active and it will still close the dialog as if the form is valid. I don’t want that OK button to work as long as required fields are not filled in.