[vishalhabib99]

profile_application and analyze_instruction_hotspots declare kernel_filter: str = None. FastMCP turns that into {"type": "string", "default": null}, so the schema advertises a default the server then refuses. A client that sends the default back explicitly, for example profile_application(command="./app", kernel_filter=null), gets:

1 validation error for call[profile_application]
kernel_filter
  Input should be a valid string [type=string_type, input_value=None, input_type=NoneType]

Some MCP clients and LLM tool callers fill in every parameter from the schema, so they hit this.

Fix

Annotations only: kernel_filter: str = None -> kernel_filter: str | None = None in both tools (1 parameter in each of 2 tools). The schema becomes anyOf: [string, null] with default: null, and both tool bodies already pass None through to Linex.profile(). ruff format wrapped the analyze_instruction_hotspots signature onto one parameter per line because the new annotation pushed it past 100 characters. Nothing else changed.

Test

Added TestToolRegistration::test_null_default_params_accept_null in linex/tests/test_mcp_server.py. It lists the registered tools and checks that every parameter whose schema says "default": null also accepts null. To share the lookup, I split the existing _registered_tools() helper into _registered_tool_objects() plus the name set; _registered_tools() returns the same names as before.

• Before the fix: fails with profile_application.kernel_filter defaults to null but rejects it
• After the fix: passes
• I checked it on fastmcp 4.1.0 and on 2.14.7 (the package pins fastmcp>=2.0.0)

Suite, pytest linex/tests on macOS (no ROCm):

	passed	failed
main	27	8
this branch	28	8

The 8 failures are the same on both: every test in test_inline_hip_sqtt.py needs hipcc and an AMD GPU, so they didn't run here. test_mcp_server.py is 28/28. ruff check and ruff format --check pass at the CI version (0.15.22).

Not included

• metrix/src/metrix/mcp/server.py has the same pattern (profile_metrics(metrics: list[str] = None)). I left it out to keep this PR to one package. Open PR Add kernel iteration selection for metrix dispatch filtering #86 already rewrites that signature as Optional[List[str]] = None, so it may not need a separate change.
• Open PR Add distributed launcher support for linex and metrix #87 adds launcher: str = None to profile_application. That parameter would have the same problem, and the two PRs touch the same signature, so whichever merges second needs a small rebase.

[mawad-amd]

Looks great. Thank you!