RNFS.downloadFile default headers

I noticed that custom headers can be set when using `downloadFile`, but I'm not entirely clear on whether the default headers will be sent either if no headers parameter is set, or in addition to those provided in the parameter?

I'm porting from `rn-fetch-blob`, which sends the same headers by default as other React Native `fetch` requests, but I'm not sure if the expected behaviour is the same here?