Throws error on :accept :json when response body is empty.

[knubie]

When you specify an :accept :json header, lambdaisland/fetch will attempt to automatically decode the response body using response.json(). However this will fail and raise an error if the response body is empty (ie JSON.parse('')).

fetch/src/lambdaisland/fetch.cljs

Lines 66 to 67 in 246d561

	(defmethod decode-body :json [_ response opts]
	(j/call response :json))

The code should probably check if the body is empty first.

[simongray]

This is sadly expected behaviour when using JS Fetch: whatwg/fetch#113

Why WHATWG didn't think this would be an issue by when they designed the API, I really have no idea. Returning 204 or 404 with no body is a common situation on the Internet and I don't think the server isn't supposed to make up imaginary content just because the client is requesting a specific content-type.

I guess this library could have a fix for us using it.

[alysbrooks]

I could see a case for a wrapper library like lambdaisland/fetch catching the error or even rethrowing a more reasonable one, but that would be an expansion to this library's scope. The code would be trivial, but semantically it would be a bit of a shift.

There is one place where we catch exceptions: https://github.com/lambdaisland/fetch/blame/926fccabfebced3340548f33e41a72b159d97678/src/lambdaisland/fetch.cljs#L106. So perhaps it wouldn't be too much of a change?