NullReferenceExceptions if using the main menus with no document open

### Describe the bug

Some of the main menu options assume that there is always a document open and will throw `NullReferenceException`s if clicked when there isn't.

It doesn't make for a great first experience if people are just clicking around to explore the interface.

### Steps to reproduce

```text
1. Launch the app for the first time (no documents open)
2a. Click "Data" in the left menu
2b. Or click "Properties" in the left menu
3. Get a NullReferenceException
```

### Expected behavior

No exceptions.

These cases should be handled without problems.

### Screenshots

_No response_

### Windows Build Number

- [ ] Windows 10 1809 (Build 17763)
- [ ] Windows 10 1903 (Build 18362)
- [ ] Windows 10 1909 (Build 18363)
- [ ] Windows 10 2004 (Build 19041)
- [ ] Windows 10 20H2 (Build 19042)
- [ ] Windows 10 21H1 (Build 19043)
- [ ] Windows 10 21H2 (Build 19044)
- [x] Windows 10 22H2 (Build 19045)
- [ ] Windows 11 21H2 (Build 22000)
- [ ] Windows 11 22H2 (Build 22621)
- [ ] Windows 11 23H2 (Build 22631)
- [ ] Windows 11 24H2 (Build 26100)
- [ ] Windows 11 25H2 (Build 26200)
- [ ] Windows 11 26H1 (Build 28000)
- [ ] Other (specify)

### Other Windows Build number

_No response_

### Additional context

PR with fixes to follow.

### Help us help you

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