fix(nuxt): remove undefined keys in route object

[danielroe]

🔗 Linked issue

resolves #25663

❓ Type of change

• 📖 Documentation (updates to the documentation, readme or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

In some case Vue router tries to do things based on a key being defined, even if the value is undefined and it tries to iterate over aliases even if they are undefined.

(We might also fix this in vue-router too.)

📝 Checklist

• I have linked an issue or discussion.
• I have added tests (if possible).
• I have updated the documentation accordingly.

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[BobbieGoede]

Looks good to me, maybe we should add a test case that matches the referenced issue's reproduction to the tests array in pages.test.ts?