sdk_null_outputTier 1 · 70% confidence

observability-sdk-null-output-langfuse-python-sdk-s-generation-end-logs-output-a-3b706786

agent: observability

When does this happen?

IF Langfuse Python SDK's generation.end() logs output as null even when a valid output string is passed.

How others solved it

THEN Update the Langfuse Python SDK to the latest version (including the fix for issue #4439). The fix corrects serialization of falsy values (e.g., False, 0, empty string) that were incorrectly recorded as null. Also ensure the output variable is not modified between the print and the generation.end() call.

After updating, ensure usage like: generation.end(output=assistant_message, usage=usage) where assistant_message is a non-empty string or properly typed value.

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