File stream is null
For some reason, my server is returning an empty stream instead of the file.

Here's the client's request:
```
-----------------------------81678640518046430391178682890
Content-Disposition: form-data; name="operations"

{"operationName":null,"variables":{"file":null},"query":"mutation ($file: Upload!) {\n  uploadUserImage(file: $file)\n}\n"}
-----------------------------81678640518046430391178682890
Content-Disposition: form-data; name="map"

{"1":["variables.file"]}
-----------------------------81678640518046430391178682890
Content-Disposition: form-data; name="1"; filename="signature.jpg"
Content-Type: image/jpeg

******** Whole Lot of data ************
-----------------------------81678640518046430391178682890--
``` 

On the server

``` Javascript
async (parent, { file }) => {  
  const { createReadStream, filename, mimetype, encoding } = await file;
  const stream = createReadStream();

  stream.on("data", data => {
      console.log("DATA**********************");
      console.log(data);      
    });

  stream.on("readable", () => {
      console.log(stream.read());
    });
}
```

Nothing gets outputted. When I send stream's data as response it returns as null.

Interestingly, filename, mimetype and encoding all are populated.

I am using [apollo-server-express](https://www.npmjs.com/package/apollo-server-express) as my server.

Here's the schema for the method

```
uploadUserImage(file: Upload!): String
```

Will really appreciate your help on this. Thanks :)