`NullReferenceException` when retrieving properties of a streaming chat chunk using Asynchronous Filter

Confirm this is not an issue with the underlying OpenAI API

[X] This is an issue with the Python library

Confirm this is not an issue with Azure OpenAI

[X] This is not an issue with Azure OpenAI

Describe the bug

When using StreamingChatCompletionUpdate with Asynchronous Filter enabled in azure, this class breaks.

https://github.com/openai/openai-dotnet/blob/583e9f6f519feeee0e2907e80bf7d5bf8302d93f/src/Custom/Chat/StreamingChatCompletionUpdate.cs#L83

When a SSE data: doesn't have a delta (null) the Choice[0].Delta line throws NullReferenceException.

Final 3 streaming chunks of an Asynchornous Filter response.

data: {"choices":[{"delta":{},"finish_reason":"stop","index":0,"logprobs":null}],"created":1724860848,"id":"chatcmpl-A1FOCU4vamBSxxqjaKcvADYMlwlaC","model":"gpt-4o-2024-05-13","object":"chat.completion.chunk","system_fingerprint":"fp_abc28019ad"}

data: {"choices":[{"content_filter_offsets":{"check_offset":1576,"start_offset":1576,"end_offset":2318},"content_filter_results":{"hate":{"filtered":false,"severity":"safe"},"self_harm":{"filtered":false,"severity":"safe"},"sexual":{"filtered":false,"severity":"safe"},"violence":{"filtered":false,"severity":"safe"}},"finish_reason":null,"index":0}],"created":0,"id":"","model":"","object":""}

data: {"choices":[{"content_filter_offsets":{"check_offset":1576,"start_offset":1576,"end_offset":2318},"content_filter_results":{"protected_material_code":{"filtered":false,"detected":false},"protected_material_text":{"filtered":false,"detected":false}},"finish_reason":null,"index":0}],"created":0,"id":"","model":"","object":""}

This issue was reported in our Semantic Kernel Issues Here but actually seems to be a problem when Azure tries to use the OpenAI SDK for those chunks, this potentially can be handled by Azure SDK library in a non-ideal (try catch block) or in the back-end (providing always an empty delta) but I wonder would be quicker/simple getting a fix in here.

The problem also happen for other properties of the class as below:

To Reproduce

Enable Asynchronous Filter in Azure or OpenAI (if possible)
Make a streaming request and try to check the Role property of the last 2 chunks

Since the property is a pointer, we are unable to test it for null.


if (lastChunk.Role.HasValue) { } // throws
if (lastChunk.Role is null) { } // throws

Code snippets

No response

OS

Windows 11

.NET version

.net 8

Library version

beta.10

openai / openai-dotnet