Passing FetchTransport in transport disable calls to collector

I am trying to send a custom header to my collector. This header is required for some reason I can not disclose here. However, using `FetchTransport` in `transports` simply stop sending requests to collector. Here is my set up

```
transports: [
new FetchTransport({
url: 'https://my-domain-com/collect',
requestOptions: {
headers: {
'my-custom-header': '16a7af77696199f3dc47a2ae4107d2b5',
},
},
}),
],
```

Not sure what is wrong? For now I am going to fork the repo and get it out.