Add fallback for pydantic v1.

backend/chainlit/langchain/callbacks.py

@@ -15,6 +15,7 @@
 from chainlit.context import context_var
 from chainlit.message import Message
 from chainlit.step import Step
+import pydantic
 
 DEFAULT_ANSWER_PREFIX_TOKENS = ["Final", "Answer", ":"]
 
@@ -125,7 +126,13 @@ def ensure_values_serializable(self, data):
                 for key, value in data.items()
             }
         elif isinstance(data, BaseModel):
-            return data.model_dump()
+            # Fallback to support pydantic v1
+            # https://docs.pydantic.dev/latest/migration/#changes-to-pydanticbasemodel
+            if pydantic.VERSION.startswith("1"):
+                return data.dict()
+
+            # pydantic v2
+            return data.model_dump()  # pyright: ignore reportAttributeAccessIssue
         elif isinstance(data, list):
             return [self.ensure_values_serializable(item) for item in data]
         elif isinstance(data, (str, int, float, bool, type(None))):