[vishalhabib99]

What breaks

Two sample MCP servers have params that default to None but are typed str:

• finance/genai-powered-financial-advisor-tools/application/mcp_server_kb.py: knowledge_base_list(region_name)
• 07-ux-demos/triage-agent/backend/mcp_servers/email_history/email_history_server.py: get_emails(subject_contains)

The generated schema advertises "default": null on a field typed string. Some agent frameworks send that default explicitly, and the call fails before the tool runs. This is the real email_history_server.py on main, called in memory with {"limit": 2, "subject_contains": null} (mcp 1.25):

isError=True  Error executing tool get_emails: 1 validation error for get_emailsArguments
subject_contains
  Input should be a valid string [type=string_type, input_value=None, input_type=NoneType]

With this change, the same call returns isError=False with {"result": []}.

Two other tools in these samples print() to stdout, which is the JSON-RPC channel on the stdio transport:

• mcp_server_stock.py: create_comparison_chart prints the chart path on every call.
• triage-agent/.../strands/strands_agent.py: real_estate_expert prints "Routed to Real Estate Expert" on every call.

A client reading stdout gets a non-JSON line (Invalid JSON: expected value at line 1 column 1). Both now print to stderr.

Change

7 lines across 4 files: Optional[str] for the two params (matching the existing typing imports) and file=sys.stderr on the two prints. No behaviour change otherwise.

Checked

• The real get_emails call above fails on main and passes on this branch.
• python -m py_compile passes on all 4 files.
• A static scan (mcp-doctor) of both sample folders reports these 4 issues before the change and none after.
• I did not run the finance or triage samples end to end, since they need AWS Bedrock credentials.