[BUG] Cannot read properties of undefined (reading 'map') - Intermittent JavaScript error in client

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code client frequently throws a JavaScript error Cannot read properties of undefined (reading
'map') during various operations, significantly impacting user experience.

What Should Happen?

API 错误：Cannot read properties of undefined (reading 'map')

Error Messages/Logs

Steps to Reproduce

Title: Cannot read properties of undefined (reading 'map') - Intermittent JavaScript error in client

Description

Claude Code client frequently throws a JavaScript error Cannot read properties of undefined (reading
'map') during various operations, significantly impacting user experience.

Error Details

API Error: Cannot read properties of undefined (reading 'map')

Reproduction

This error occurs intermittently during:

• File operations (grep, find, read, write)
• MCP tool usage
• Basic command execution
• Multi-step operations

Frequency: ~20-30% of operations (highly reproducible)

Environment

• Claude Code Version: 1.0.123
• Platform: macOS (Darwin 25.0.0)
• MCP Servers: magic, context7, gemini-cli, qwen-cli (serena failed to connect)

Expected vs Actual Behavior

• Expected: Operations complete successfully
• Actual: Random failure with undefined map error

Technical Analysis

This appears to be a client-side JavaScript bug where:

1. Some internal operation returns undefined instead of expected array
2. Subsequent code calls .map() on undefined without null checking
3. Error manifests as "Cannot read properties of undefined (reading 'map')"

Impact

• Disrupts normal workflow
• Requires frequent session restarts
• Affects both simple and complex operations
• Creates user frustration and productivity loss

Workaround

Currently using operation decomposition and retry strategies, but this is not a sustainable solution.

Request

Please add proper null/undefined checking before calling .map() method in the client codebase. This
would prevent the error and improve overall stability.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.0.123

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_