fix(langchain): convert invalid_tool_calls to ToolCallSchema and skip empty lists

- Apply the same {id, type, name, arguments, error} conversion to
  invalid_tool_calls as is done for tool_calls
- Only assign tool_calls / invalid_tool_calls to message_dict when the
  converted list is non-empty

Author: udayshnk

langfuse/langchain/CallbackHandler.py

@@ -1122,14 +1122,40 @@ def _convert_message_to_dict(self, message: BaseMessage) -> Dict[str, Any]:
                             "arguments": arguments,
                         }
                     )
-                message_dict["tool_calls"] = converted_tool_calls
+                if converted_tool_calls:
+                    message_dict["tool_calls"] = converted_tool_calls
 
             if (
-                hasattr(message, "invalid_tool_calls") 
-                and message.invalid_tool_calls is not None 
+                hasattr(message, "invalid_tool_calls")
+                and message.invalid_tool_calls is not None
                 and len(message.invalid_tool_calls) > 0
             ):
-                message_dict["invalid_tool_calls"] = message.invalid_tool_calls
+                converted_invalid_tool_calls = []
+                for tc in message.invalid_tool_calls:
+                    if not isinstance(tc, dict):
+                        langfuse_logger.debug(
+                            "Skipping invalid_tool_call entry that is not a dict: %s",
+                            tc,
+                        )
+                        continue
+                    try:
+                        arguments = json.dumps(tc.get("args", {}))
+                    except (TypeError, ValueError) as e:
+                        langfuse_logger.debug(
+                            "Failed to serialize invalid tool call args to JSON: %s", e
+                        )
+                        arguments = "{}"
+                    converted_invalid_tool_calls.append(
+                        {
+                            "id": tc.get("id", ""),
+                            "type": "function",
+                            "name": tc.get("name", ""),
+                            "arguments": arguments,
+                            "error": tc.get("error", ""),
+                        }
+                    )
+                if converted_invalid_tool_calls:
+                    message_dict["invalid_tool_calls"] = converted_invalid_tool_calls
 
         elif isinstance(message, SystemMessage):
             message_dict = {"role": "system", "content": message.content}