Nucleus does not handle delta publish artifacts from electron-forge

I'm trying to configure electron-forge to upload artifacts to nucleus as it seems like a great solution, however every time I try to release a set of release artifacts I encounter a problem.

The delta updates are being built and uploaded fine but when releasing the following output is shown:

```
nucleus_1 | Mon, 11 May 2020 08:09:10 GMT nucleus:rest TypeError: Cannot read property 'toUpperCase' of null
nucleus_1 | at Object. (/opt/service/lib/files/utils/win32.js:25:44)
nucleus_1 | at Generator.next ()
nucleus_1 | at fulfilled (/opt/service/lib/files/utils/win32.js:4:58)
nucleus_1 | at
nucleus_1 | Mon, 11 May 2020 08:09:10 GMT nucleus:rest Fetching temporary releases for app: brl and channel: Stable
nucleus_1 | Mon, 11 May 2020 08:09:10 GMT nucleus:rest Listing applications
```

The property that it's talking about is the `sha1` property. I desperately want to use nucleus but if delta updates are not working then that's a hard pill to swallow.

Interestingly enough updates are all good when not doing delta updates and just uploading 2 full packages.

Start with lib/files/utils/win32.js at the reported line and trace how delta artifacts from electron-forge populate the sha1 property during release. Compare the metadata from delta uploads with the two full-package case, then reproduce the release failure and verify the release no longer throws the toUpperCase-on-null error.

Written by the indexing model from the issue text.