OutputSchema in ResiterTool can only take non-nullable schema

[hanfangAmazon]

Describe the bug

Sometimes the output can be either undefined/null or have a value that matches the shchema, but OutputSchema config only takes ZodRawShape and convert it to Zod object here

typescript-sdk/src/server/mcp.ts

Line 645 in 1878143

outputSchema === undefined ? undefined : z.object(outputSchema),

That whay I can't return undefined or null in callback handler, which are considered as a valid output as well.

Expected behavior
OutputSchema should allow null/undefined response, or allow us to pass Zod object directly