[BUG] Azure.AI.Agents.Persistent NullReferenceException after successful streamed response finalization

[brandonh-msft]

Bug description

When using Azure.AI.Agents.Persistent through Microsoft Agent Framework streaming APIs, a chat run can complete successfully, return the full assistant answer, and then crash during stream finalization/disposal with a System.NullReferenceException.

The exception originates inside the Azure SDK telemetry/finalization path:
Azure.AI.Agents.Persistent.RunStepOpenAPIToolCall.JsonModelWriteCore(...)

Package and environment

• Package: Azure.AI.Agents.Persistent
• Package version: 1.0.0-preview.260311.1
• App shape: .NET 10 console app using Microsoft Agent Framework with Azure Foundry persistent agents
• OS: Windows
• Auth: DefaultAzureCredential
• Streaming path: AIAgent.RunStreamingAsync(...)

Expected behavior

After the streamed answer completes, enumeration/disposal should finish cleanly.

Actual behavior

The full assistant answer is returned to the caller, but the process crashes afterward during stream cleanup/final telemetry processing.

Reproduction notes

1. Create a persistent Foundry agent and connect with PersistentAgentsClient / ChatClientAgent.
2. Wrap the agent with Agent Framework OpenTelemetry instrumentation.
3. Call RunStreamingAsync(...) and enumerate the response stream to completion.
4. Observe that, after the final assistant output is emitted, the SDK throws NullReferenceException during finalization.

Minimal observed output

assistant(stream)> <full answer omitted>
[update] role=assistant, messageId=..., author=..., responseId=...
[update] role=assistant, messageId=..., author=..., responseId=...
[content:UsageContent] Microsoft.Extensions.AI.UsageContent
Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at Azure.AI.Agents.Persistent.RunStepOpenAPIToolCall.JsonModelWriteCore(Utf8JsonWriter writer, ModelReaderWriterOptions options)
   at Azure.AI.Agents.Persistent.RunStepOpenAPIToolCall.System.ClientModel.Primitives.IJsonModel<Azure.AI.Agents.Persistent.RunStepOpenAPIToolCall>.Write(...)
   at Azure.AI.Agents.Persistent.ModelSerializationExtensions.WriteObjectValue[T](...)
   at Azure.AI.Agents.Persistent.RunStepOpenAPIToolCall.ToRequestContent()
   at Azure.AI.Agents.Persistent.Telemetry.OpenTelemetryScope.GetToolCallAttributes(RunStepToolCall toolCall)
   at Azure.AI.Agents.Persistent.Telemetry.OpenTelemetryScope.ProcessToolCalls(RunStepToolCallDetails toolCallDetails)
   at Azure.AI.Agents.Persistent.Telemetry.OpenTelemetryScope.RecordRunStepEventAttributes(RunStep runStep, Boolean stream)
   at Azure.AI.Agents.Persistent.Telemetry.OpenTelemetryScope.End()
   at Azure.AI.Agents.Persistent.Telemetry.OpenTelemetryScope.Dispose()

Suspected root cause

The generated serializer for RunStepOpenAPIToolCall appears to iterate OpenAPI without a null check.

Relevant file: sdk/ai/Azure.AI.Agents.Persistent/src/Generated/RunStepOpenAPIToolCall.Serialization.cs

Impact

• The user-visible answer is already complete, but the client process still terminates.
• This makes streamed chat runs unreliable in production.
• The issue appears tied to SDK finalization/telemetry, not application rendering.

Workaround currently used

Application-side workaround: catch this very specific NullReferenceException after the stream completes and preserve the completed answer.

Request

Please confirm whether this is a known bug in Azure.AI.Agents.Persistent preview and whether a null-safe fix should be added around RunStepOpenAPIToolCall serialization / telemetry attribute generation.

[nick863]

The issue has been fixed in the new version of SDK. Please upgrade to the latest version using command:

dotnet add package Azure.AI.Agents.Persistent --version 1.2.0-beta.10

Please let us know if it has solved the problem.

[github-actions]

Hi @brandonh-msft. Thank you for opening this issue and giving us the opportunity to assist. We believe that this has been addressed. If you feel that further discussion is needed, please add a comment with the text "/unresolve" to remove the "issue-addressed" label and continue the conversation.