Failed to fetch with undefined headers

[Cheng You Bai (:cybai)]

When I tried to use `fetch` with `undefined` headers, the promise will be rejected with `TypeError: undefined is not an object`.

Ex. `fetch('/my-awesome-api', { headers: undefined })`

```
TypeError: undefined is not an object
anonymous
fillFetchHeaders
initializeFetchRequest
[native code]
fetch
tryCatch
invoke
step
(anonymous function)
run
(anonymous function)
flush
```

I'm using OSX 10.11 El Capitan and on Safari 10.1 (11603.1.30.0.34).

I know there's another [bugzilla issue](https://bugs.webkit.org/show_bug.cgi?id=168043) about this issue.
However, I still face this issue.

If the fix is released yet, please kindly help me to close this issue.

Thanks.

[youenn fablet]

The next Safari release will probably include it.
In the meantime, could you use a workaround like not setting the "headers" key when its value would be undefined?

[Cheng You Bai (:cybai)]

Hi youenn fablet,

Yes, I've tried to use empty object to handle this issue and it works fine.

Ex.
``` 
fetch('/my-awesome-api', { headers: headers || {} });
```

Hope it will be released soon, thanks!

[youenn fablet]

Closing bug as fixed. Please reopen if needed.