Bug: TypeError when processing empty input array

Question

When passing an empty array to the CLI parser, it throws a TypeError instead of returning gracefully.

**Steps to reproduce:**
1. Run `codex exec "process this: []"`
2. Observe the error output

**Expected behavior:**
Should return an empty result or a helpful message.

**Actual behavior:**
```
TypeError: Cannot read properties of undefined (reading 'length')
```

**Environment:**
- codex v1.0.2
- macOS 14.5
- Node.js 22.1.0

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