[Bug]: App crash when clicking on create new "Sold Appliance" button

### Preflight Checklist

- [x] I have read the [Contributing Guidelines](https://github.com/EnAccess/micropowermanager-agent-app/blob/main/CONTRIBUTING.md) for this project, if it exists.
- [x] I agree to follow the [Code of Conduct](https://github.com/EnAccess/micropowermanager-agent-app/blob/main/CODE_OF_CONDUCT.md) that this project adheres to.
- [x] I have searched the [issue tracker](https://github.com/EnAccess/micropowermanager-agent-app/issues) for a feature request that matches the one I want to file, without success.

### Expected Behavior

The Agent app should open the new sold appliance view without crashing.

### Actual Behavior

Crashed with error traceback below

### Steps to reproduce

1. Go to Customer list view
2. Click on customer detail
3. Click on "Appliance" section on bottom pane
4. Click on new button

### What operating system(s) are you using?

macOS

### Additional Information

_No response_