Drop assertion on Google streaming (#2618)

Author: Kludex

pydantic_ai_slim/pydantic_ai/models/google.py

@@ -219,7 +219,7 @@ async def count_tokens(
         )
         if self._provider.name != 'google-gla':
             # The fields are not supported by the Gemini API per https://github.com/googleapis/python-genai/blob/7e4ec284dc6e521949626f3ed54028163ef9121d/google/genai/models.py#L1195-L1214
-            config.update(
+            config.update(  # pragma: lax no cover
                 system_instruction=generation_config.get('system_instruction'),
                 tools=cast(list[ToolDict], generation_config.get('tools')),
                 # Annoyingly, GenerationConfigDict has fewer fields than GenerateContentConfigDict, and no extra fields are allowed.
@@ -535,9 +535,8 @@ async def _get_event_iterator(self) -> AsyncIterator[ModelResponseStreamEvent]:
                     raise UnexpectedModelBehavior('Safety settings triggered', str(chunk))
                 else:  # pragma: no cover
                     raise UnexpectedModelBehavior('Content field missing from streaming Gemini response', str(chunk))
-
-            assert candidate.content.parts is not None
-            for part in candidate.content.parts:
+            parts = candidate.content.parts or []
+            for part in parts:
                 if part.text is not None:
                     if part.thought:
                         yield self._parts_manager.handle_thinking_delta(vendor_part_id='thinking', content=part.text)

pydantic_ai_slim/pydantic_ai/usage.py

@@ -292,7 +292,7 @@ def check_before_request(self, usage: RunUsage) -> None:
 
         total_tokens = usage.total_tokens
         if self.total_tokens_limit is not None and total_tokens > self.total_tokens_limit:
-            raise UsageLimitExceeded(
+            raise UsageLimitExceeded(  # pragma: lax no cover
                 f'The next request would exceed the total_tokens_limit of {self.total_tokens_limit} ({total_tokens=})'
             )
 

tests/models/test_google.py

@@ -1670,7 +1670,9 @@ async def test_google_model_usage_limit_not_exceeded(allow_model_requests: None,
 """)
 
 
-async def test_google_vertexai_model_usage_limit_exceeded(allow_model_requests: None, vertex_provider: GoogleProvider):
+async def test_google_vertexai_model_usage_limit_exceeded(
+    allow_model_requests: None, vertex_provider: GoogleProvider
+):  # pragma: lax no cover
     model = GoogleModel('gemini-2.0-flash', provider=vertex_provider, settings=ModelSettings(max_tokens=100))
 
     agent = Agent(model, system_prompt='You are a chatbot.')