[Geneva Exporter] Check usage of `unwrap()`

[utpilla]

We must inspect the usage of unwrap() in Geneva Uploader to ensure that there would be no panics at runtime.

Check the usage here for reference.

1. We should try to avoid using unwrap() altogether either by checking the underlying value or provide some default with unwrap_or etc.
2. For cases, where it's guaranteed that unwrap() would not result in panic, we should add a comment about safety and replace unwrap() with expect().