[BUG] Claude Desktop MCP fails on all parameterized calls for filesystem tool — "Cannot convert undefined or null to object"

Environment

• Platform (select one):
• Claude Desktop with MCP [Claude CLI Code works fine — this bug occurs only in the Desktop app]

Bug Description

Claude Desktop fails consistently on all parameter-based MCP operations for the @modelcontextprotocol/server-filesystem tool, including:

• read\_file
• get\_file\_info
• directory\_tree
• search\_files

Only list_directory (which requires no parameters) succeeds.

The error returned is:

Error executing code: Cannot convert undefined or null to object

This issue does not occur in Claude CLI, suggesting the problem is specific to Claude Desktop’s parameter serialization or transmission layer.

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Expected Behavior

• File and directory operations with valid parameters should execute normally.
• MCP tools should receive properly serialized arguments.
• Behavior should be consistent between Claude CLI and Claude Desktop.

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Actual Behavior

• list_directory works correctly (no parameters).
• All parameter-based operations fail with serialization errors.
• Works flawlessly on Claude CLI with the same configuration and tool.

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🛠️ Troubleshooting Attempted

• ✅ Verified MCP server output
• ✅ Confirmed correct ~/.claude/mcp.config.json
• ✅ Used absolute file paths
• ✅ Restarted Claude Desktop and MCP multiple times
• ✅ Confirmed functionality in Claude CLI
• ❌ No workaround found — issue persists in all Desktop sessions

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🧾 Configuration Used

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": [
        "-y",
        "@modelcontextprotocol/server-filesystem",
        "/Users/{MyName}"
      ]
    }
  }
}

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Technical Analysis

The error message:
TypeError: Cannot convert undefined or null to object

suggests that the parameter object passed from Claude Desktop is either missing or not properly constructed. This usually happens in JavaScript when:

• Object.keys(), Object.entries() or Object.assign() are called on undefined
• Destructuring is attempted on null/undefined

Since list_directory (no params) works, but read_file (needs path) fails, this is likely due to MCP parameter serialization logic breaking down inside Claude Desktop.

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Affected Operations

• ✅ list\_directory: success
• ❌ read\_file: fails
• ❌ get\_file\_info: fails
• ❌ directory\_tree: fails
• ❌ search\_files: fails

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System Info

• Claude Desktop Version: Claude 0.12.28 (5f9bc7) — 2025-07-18T21:14:50.000Z
• Claude CLI: All MCP operations work as expected
• Operating System: macOS 15.4.1 (Sequoia) Build 24E263
• Node.js Version: v22.17.1
• npm Version: 10.9.2
• Terminal: macOS Terminal & iTerm2

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Related Issues

• This appears related to https://github.com/anthropics/claude-code/issues/4195

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Priority

🔴 High — prevents any meaningful use of MCP in Claude Desktop for parameter-based tools.
Workflows relying on file reading, writing, or searching are completely blocked.