openai[patch]: Improve error message when response type is malformed (#31619)

libs/partners/openai/langchain_openai/chat_models/base.py

@@ -1111,15 +1111,27 @@ class BaseChatOpenAI(BaseChatModel):
         response_dict = (
             response if isinstance(response, dict) else response.model_dump()
         )
-        # Sometimes the AI Model calling will get error, we should raise it.
-        # Otherwise, the next code 'choices.extend(response["choices"])'
-        # will throw a "TypeError: 'NoneType' object is not iterable" error
-        # to mask the true error. Because 'response["choices"]' is None.
+        # Sometimes the AI Model calling will get error, we should raise it (this is
+        # typically followed by a null value for `choices`, which we raise for
+        # separately below).
         if response_dict.get("error"):
             raise ValueError(response_dict.get("error"))
 
+        # Raise informative error messages for non-OpenAI chat completions APIs
+        # that return malformed responses.
+        try:
+            choices = response_dict["choices"]
+        except KeyError as e:
+            raise KeyError(
+                f"Response missing `choices` key: {response_dict.keys()}"
+            ) from e
+
+        if choices is None:
+            raise TypeError("Received response with null value for `choices`.")
+
         token_usage = response_dict.get("usage")
-        for res in response_dict["choices"]:
+
+        for res in choices:
             message = _convert_dict_to_message(res["message"])
             if token_usage and isinstance(message, AIMessage):
                 message.usage_metadata = _create_usage_metadata(token_usage)