Fatal crash: Cannot read properties of undefined (reading 'join') when notebook exists in library

[obaind]

Bug Description

When any notebook is added to the library, the MCP server crashes on startup with:

TypeError: Cannot read properties of undefined (reading 'join')
    at buildAskQuestionDescription (notebooklm-mcp/dist/tools/definitions/ask-question.js:8:38)
    at buildToolDefinitions (notebooklm-mcp/dist/tools/definitions.js:17:22)

Steps to Reproduce

1. Install via npx notebooklm-mcp@latest (also tested with @1.2.1)
2. Run setup_auth - works fine
3. Run add_notebook(url: "...", name: "Test", tags: ["test"]) - works fine
4. Run ask_question(question: "...") - crashes

Expected Behavior

Should query the notebook and return a response.

Actual Behavior

Server crashes immediately on any tool call once a notebook exists in library.json.

Environment

• macOS (arm64)
• Node.js v25.4.0
• notebooklm-mcp v1.2.1 (also tested v1.0.0)
• Using via mcporter MCP client

Workaround

Deleting ~/Library/Application Support/notebooklm-mcp/library.json allows the server to start, but then notebooks can't be used.

Library.json Content (when crash occurs)

{
  "notebooks": [{
    "id": "test",
    "url": "https://notebooklm.google.com/notebook/...",
    "name": "Test",
    "content_types": ["documentation", "examples"],
    "use_cases": ["Learning about Test", "Implementing features with Test"],
    "tags": ["test"],
    ...
  }],
  "active_notebook_id": "test",
  ...
}

Seems like buildAskQuestionDescription is accessing an undefined property and calling .join() on it.