deserialize null faithfully

[deyaaeldeen]

Currently core-http deserialize empty body response with a default value and not a null (here is an example). The reason we do not deserialize to null is we always attach a _response information to our response values and this is not possible with a null. In order to faithfully deserialize values coming form the server, we need to change the representation of _response. This should be taken into consideration in this issue: #10887. Because it is a breaking change, it should be planned for core-http v2.

[HarshaNalluru]

So, the "null" response would not have a corresponding _response?

[deyaaeldeen]

@HarshaNalluru _response is added to the response using intersection types and the intersection of _response and null, is, yes you guessed it right, never. We sidestep the issue by not returning a null to begin with. To fix this and faithfully deserialize the response, we need to change our representation of the response to either make the the information in _response on-demand using a callback like what Python SDK does or wrap it around the actual value using what .Net SDK does. Any other suggestions are welcome too!

[xirzec]

consider for #8535

[deyaaeldeen]

_response has been moved to be accessible through a callback in core-client. I think what remains to be done is to make sure we deserialize nulls as nulls in core-https.