mcp_field(None, ...) already yields None, so the extra None guard is dead.
Drop the #121042 KNOWN entry from the stdio conformance suite: on a
trust: untrusted server the readOnlyHint tool now runs without approval
against the real mcp 2.x fixture server.
Co-authored-by: pierrenode <298902573+pierrenode@users.noreply.github.com>