serializer has a bad design (express-bff)

[pyoner]

We use a serializer to prevent JSON Circular Reference Error, but in the initialization stage of SSE (express-bff) we pass an instance of serializer.

The serializer instance has its own state until the application is restarted.
The problem: serializer returns null every time it found a value in WeakSet for different json data.

See 6856d94

I think serializer should replace a default JSON.stringify code in the express-bff

data = serializer ? serializer(data) : JSON.stringify(data);

@blokhin

[blokhin]

discussed in PaulMaly/express-bff#5