Fix Azure OpenAI streaming when async content filter is enabled

pydantic_ai_slim/pydantic_ai/models/openai.py

@@ -1171,6 +1171,9 @@ async def _get_event_iterator(self) -> AsyncIterator[ModelResponseStreamEvent]:
             except IndexError:
                 continue
 
+            if choice.delta is None:  # pyright: ignore[reportUnnecessaryComparison]
+                continue
+
             # Handle the text part of the response
             content = choice.delta.content
             if content is not None:

tests/models/test_openai.py

@@ -603,6 +603,37 @@ async def test_no_delta(allow_model_requests: None):
         assert result.usage() == snapshot(RunUsage(requests=1, input_tokens=6, output_tokens=3))
 
 
+def none_delta_chunk(finish_reason: FinishReason | None = None) -> chat.ChatCompletionChunk:
+    choice = ChunkChoice(index=0, delta=ChoiceDelta())
+    # When using Azure OpenAI and an async content filter is enabled, the openai SDK can return None deltas.
+    choice.delta = None  # pyright: ignore[reportAttributeAccessIssue]
+    return chat.ChatCompletionChunk(
+        id='x',
+        choices=[choice],
+        created=1704067200,  # 2024-01-01
+        model='gpt-4o',
+        object='chat.completion.chunk',
+        usage=CompletionUsage(completion_tokens=1, prompt_tokens=2, total_tokens=3),
+    )
+
+
+async def test_none_delta(allow_model_requests: None):
+    stream = [
+        none_delta_chunk(),
+        text_chunk('hello '),
+        text_chunk('world'),
+    ]
+    mock_client = MockOpenAI.create_mock_stream(stream)
+    m = OpenAIChatModel('gpt-4o', provider=OpenAIProvider(openai_client=mock_client))
+    agent = Agent(m)
+
+    async with agent.run_stream('') as result:
+        assert not result.is_complete
+        assert [c async for c in result.stream_text(debounce_by=None)] == snapshot(['hello ', 'hello world'])
+        assert result.is_complete
+        assert result.usage() == snapshot(RunUsage(requests=1, input_tokens=6, output_tokens=3))
+
+
 @pytest.mark.filterwarnings('ignore:Set the `system_prompt_role` in the `OpenAIModelProfile` instead.')
 @pytest.mark.parametrize('system_prompt_role', ['system', 'developer', 'user', None])
 async def test_system_prompt_role(