Error handling empty responses in `.json()`

[BerniWittmann]

When the response body is empty aka response.bodyString === '' then calling response.json() does cause an Unexpected end of json error, since apparently this function cannot handle this edge case.

Reproduction:

1. Simple Endpoint that returns some json body -> everything works
2. Simple endpoint that returns nothing (not even an empty json object {} -> Unexpected end of json` error

a simple workaround for now is response.bodyString.length > 0 ? await response.json() : {}, but that should not be the intended use. I suggest doing a check at the beginning of this json function