Serialized class as member of another class has no values

[wvffle]

Bug description

It's hard to explain but when I tried to serialize class that contained another instance of the same class in itself then values of inner class didn't get serialized

Snippet

https://runkit.com/embed/gq92p5obr25x

It's good to mention that this not only doesn't work when double array is used but also following doesn't work:

ser.stringify(new S(new S({ a: 1, b: 2 })))