fix: exclude None optional fields from task result serialization#2544
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abhinavmathur-atlan wants to merge 1 commit intomodelcontextprotocol:mainfrom
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model_dump() without exclude_none=True emits null for optional fields (e.g. TextContent.annotations), breaking Node SDK Zod validation which marks those fields as optional/absent rather than nullable. Matches the exclude_none=True, mode="json" convention used throughout the rest of the session layer's serialization paths. Fixes modelcontextprotocol#2539
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@maxisbey @Kludex @felixweinberger , when you get a chance, this is a small fix (2 lines + test) for #2539. Happy to adjust if anything looks off. |
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Summary
Fixes #2539
task_result_handler.pycalledmodel_dump(by_alias=True)withoutexclude_none=True, causing optional fields likeTextContent.annotationsto be emitted as JSONnull. The Node SDK Zod schema marks these fields as optional (absent), not nullable, so receivingnullfails validation.Root cause: The
result_datadict built at line 119 carriednullvalues intoGetTaskPayloadResult.model_validate(). SinceGetTaskPayloadResultusesextra="allow", the nested content is stored as raw dict values — the transport-levelexclude_none=Truedoes not recursively clean them.Fix: Add
exclude_none=True, mode="json"to bothmodel_dump()calls in the terminal-state path, consistent with every other serialization site inshared/session.pyandserver/session.py.Changes
src/mcp/server/experimental/task_result_handler.py: addexclude_none=True, mode="json"toresult.model_dump(), andexclude_none=Truetorelated_task.model_dump()tests/experimental/tasks/server/test_task_result_handler.py: regression test assertingannotationsand_metaare absent (not null) in the serialized wire output