useRouteParams not using default value for empty optional params

[TheVaan]

Describe the bug

An optional param is resolved as an empty string not as undefined. Because of this, userRouteParams('param', 'default') won't return default but an empty string.

Setting a default value if param is missing is useless, when optional parameters are always empty string.

Reproduction

https://stackblitz.com/edit/vitejs-vite-157rjb

System Info

System:
    OS: macOS 14.4.1
    CPU: (10) arm64 Apple M1 Pro
    Memory: 123.70 MB / 32.00 GB
    Shell: 3.7.0 - /opt/homebrew/bin/fish
  Binaries:
    Node: 20.11.1 - ~/.nvm/versions/node/v20.11.1/bin/node
    npm: 10.5.2 - ~/.nvm/versions/node/v20.11.1/bin/npm
  Browsers:
    Chrome: 124.0.6367.61
    Edge: 124.0.2478.51
    Firefox: 124.0.2
    Safari: 17.4.1

Used Package Manager

npm

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a VueUse issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to https://github.com/vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion.
• The provided reproduction is a minimal reproducible example of the bug.