Fix: Error.Cause() returning itself

[mrizk]

Description

Error.Cause() currently returns itself if there's no ErrCause set, which when passed into pkg/errors.Cause() leads to an infinite busy loop.

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 💥 Breaking change
• 📝 Documentation
• ♻️ Refactoring
• ⚡ Performance
• ✅ Tests
• 🔧 Build/CI

Related Issue

None

Changes

• Return nil if an Error has no ErrCause
• Add unit tests to verify fix.

Checklist

• My code adheres to the coding and style guidelines of the project.
• I have performed a self-review of my own code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.

Notes

Could be a breaking change if some caller somewhere relies on Cause() never returning nil.

[mrizk]

FYI @franklinkim
also here's the related keel fix: foomo/keel#305