Fix handling of formulae and casks with null homepage values

[Copilot]

Problem

Brew-explorer was crashing when encountering formulae or casks with null homepage values in the Homebrew JSON response. This caused a deserialization error:

Error loading packages from Homebrew: invalid type: null, expected a string at line 4037 column 22

Example of a formulae with null homepage: deterministic-zip

Solution

Updated the data structures and conversion logic to properly handle null homepage values:

1. Changed homepage field type: Modified BrewFormula and BrewCask structs to use Option<String> instead of String for the homepage field, allowing null values from JSON
2. Added fallback value: When a null homepage is encountered, the application now displays "No homepage available" instead of crashing
3. Updated all conversion paths: Ensured both the From trait implementations and the refresh_package method handle null homepages correctly

Testing

Added comprehensive tests to verify the fix:

• Deserialization tests for null homepage in both formulae and casks
• Conversion tests ensuring PackageInfo correctly uses the fallback value
• All existing tests continue to pass

The application now gracefully handles packages without homepage information whilst maintaining full functionality for packages that do provide this field.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Formulae with null as homepage not handled.</issue_title>
<issue_description>If a formulae has a homepage that is null, then brew explorer fails to load:

Example of formulae with null as homepage: https://github.com/timo-reymann/deterministic-zip </issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #18

---

💬 Share your feedback on Copilot coding agent for the chance to win a $200 gift card! Click here to start the survey.