Code Review Assistant

Review this code and provide feedback:

```[LANGUAGE]
[PASTE CODE HERE]
```

Analyze for:
1. **Bugs & Edge Cases** - potential runtime errors, null checks, boundary conditions
2. **Performance** - inefficiencies, unnecessary operations, O(n) improvements
3. **Security** - injection risks, data validation, authentication gaps
4. **Readability** - naming, structure, comments needed
5. **Best Practices** - design patterns, SOLID principles

For each issue found, provide:
- Line number(s)
- Problem description
- Suggested fix with code snippet