[fetch] Should `body` parameter in the Response constructor nullable? (#178)

Currently the type of `body` parameter in the Response constructor is `optional BodyInit`. That means we cannot create a null body response with specifying the second `init` parameter.

Reported at https://code.google.com/p/chromium/issues/detail?id=524500.
Declaring the parameter as nullable fixes it, I think.

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/178