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

Author: sjrl

integrations/langfuse/src/haystack_integrations/tracing/langfuse/tracer.py

@@ -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 [])]
                 if isinstance(gen_kwargs := value.get("generation_kwargs"), dict):
                     self._span.update(input={"messages": messages, "generation_kwargs": gen_kwargs})
                 else:
@@ -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)

integrations/langfuse/tests/test_tracer.py

@@ -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):