Update check (#6020)

We were assigning the name as None in on_chat_model_start then not
updating, resulting in a validation error.

langchain/callbacks/tracers/langchain.py

@@ -53,7 +53,6 @@ class LangChainTracer(BaseTracer):
         execution_order = self._get_execution_order(parent_run_id_)
         chat_model_run = Run(
             id=run_id,
-            name=serialized.get("name"),
             parent_run_id=parent_run_id,
             serialized=serialized,
             inputs={"messages": [messages_to_dict(batch) for batch in messages]},

langchain/callbacks/tracers/schemas.py

@@ -123,7 +123,7 @@ class Run(RunBase):
     @root_validator(pre=True)
     def assign_name(cls, values: dict) -> dict:
         """Assign name to the run."""
-        if "name" not in values:
+        if values.get("name") is None:
             if "name" in values["serialized"]:
                 values["name"] = values["serialized"]["name"]
             elif "id" in values["serialized"]: