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fix: Fix langfuse tracer when input messages is None #3324

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Merged
sjrl merged 2 commits into from
May 18, 2026
+23 −4
Merged

fix: Fix langfuse tracer when input messages is None #3324

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94a2d8a
fix case where messages returns a None value instead of a list
sjrl May 18, 2026
4026e82
also catch same potential issue in replies being None (not likely to …
sjrl May 18, 2026
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9 changes: 5 additions & 4 deletions integrations/langfuse/src/haystack_integrations/tracing/langfuse/tracer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -90,7 +90,7 @@ def set_content_tag(self, key: str, value: Any) -> None:
return
if key.endswith(".input"):
if "messages" in value:
messages = [m.to_openai_dict_format(require_tool_call_ids=False) for m in value["messages"]]
messages = [m.to_openai_dict_format(require_tool_call_ids=False) for m in (value.get("messages") or [])]
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@sjrl sjrl May 18, 2026

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We do value.get("messages") or [] to catch the case that messages key is present in value but it returns None. Doing value.get("messages", []) would not catch it since the back up [] only occurs if messages is missing.

if isinstance(gen_kwargs := value.get("generation_kwargs"), dict):
self._span.update(input={"messages": messages, "generation_kwargs": gen_kwargs})
else:
Expand All @@ -100,10 +100,11 @@ def set_content_tag(self, key: str, value: Any) -> None:
self._span.update(input=coerced_value)
elif key.endswith(".output"):
if "replies" in value:
if all(isinstance(r, ChatMessage) for r in value["replies"]):
replies = [m.to_openai_dict_format(require_tool_call_ids=False) for m in value["replies"]]
replies_list = value.get("replies") or []
if all(isinstance(r, ChatMessage) for r in replies_list):
replies = [m.to_openai_dict_format(require_tool_call_ids=False) for m in replies_list]
else:
replies = value["replies"]
replies = replies_list
self._span.update(output=replies)
else:
coerced_value = tracing_utils.coerce_tag_value(value)
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18 changes: 18 additions & 0 deletions integrations/langfuse/tests/test_tracer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -180,6 +180,24 @@ def test_set_content_tag_updates_input_and_output_with_messages(self):
# check we handle properly string list replies
assert mock_context_manager._span.update.call_args_list[0][1] == {"output": ["reply1", "reply2"]}

def test_set_content_tag_messages_none_does_not_raise(self):
mock_context_manager = MockContextManager()
span = LangfuseSpan(mock_context_manager)

with patch("haystack_integrations.tracing.langfuse.tracer.proxy_tracer.is_content_tracing_enabled", True):
span.set_content_tag("key.input", {"messages": None})
assert mock_context_manager._span.update.call_count == 1
assert mock_context_manager._span.update.call_args_list[0][1] == {"input": []}

def test_set_content_tag_replies_none_does_not_raise(self):
mock_context_manager = MockContextManager()
span = LangfuseSpan(mock_context_manager)

with patch("haystack_integrations.tracing.langfuse.tracer.proxy_tracer.is_content_tracing_enabled", True):
span.set_content_tag("key.output", {"replies": None})
assert mock_context_manager._span.update.call_count == 1
assert mock_context_manager._span.update.call_args_list[0][1] == {"output": []}


class TestSpanContext:
def test_post_init(self):
Expand Down
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