fix: address review feedback on PR #32103

Fixed both P1 edge cases Greptile flagged in _get_mock_response_content (empty choices list and None message content) by returning an empty string to still short-circuit rather than crashing or falling through to the real model, and added two regression tests covering them.

litellm/llms/anthropic/experimental_pass_through/messages/handler.py

@@ -368,9 +368,12 @@ def _get_mock_response_content(
     if isinstance(mock_response, str):
         return mock_response
     if isinstance(mock_response, litellm.ModelResponse):
+        if not mock_response.choices:
+            return ""
         first_choice = mock_response.choices[0]
         if isinstance(first_choice, litellm.Choices):
-            return first_choice.message.content
+            return first_choice.message.content or ""
+        return ""
     return None
 
 

tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_anthropic_experimental_pass_through_messages_handler.py

@@ -676,6 +676,55 @@ def test_handler_short_circuits_on_model_response_mock_response():
     assert result["content"][0]["text"] == "Blocked by guardrail"
 
 
+def test_handler_short_circuits_on_model_response_with_empty_choices():
+    """A ModelResponse mock with no choices must still short-circuit instead
+    of crashing on an unguarded choices[0] access."""
+    from litellm.llms.anthropic.experimental_pass_through.messages import handler
+
+    blocked_response = ModelResponse(choices=[], model="bedrock-guardrail")
+
+    with patch.object(
+        handler.base_llm_http_handler,
+        "anthropic_messages_handler",
+    ) as mock_base_handler:
+        result = handler.anthropic_messages_handler(
+            max_tokens=10,
+            messages=[{"role": "user", "content": "some blocked content"}],
+            model="anthropic/claude-3-5-sonnet-20241022",
+            custom_llm_provider="anthropic",
+            mock_response=blocked_response,
+        )
+
+    mock_base_handler.assert_not_called()
+    assert result["content"][0]["text"] == ""
+
+
+def test_handler_short_circuits_on_model_response_with_none_content():
+    """A ModelResponse mock whose message content is None must still
+    short-circuit rather than silently falling through to the real model."""
+    from litellm.llms.anthropic.experimental_pass_through.messages import handler
+
+    blocked_response = ModelResponse(
+        choices=[Choices(message=Message(content=None))],
+        model="bedrock-guardrail",
+    )
+
+    with patch.object(
+        handler.base_llm_http_handler,
+        "anthropic_messages_handler",
+    ) as mock_base_handler:
+        result = handler.anthropic_messages_handler(
+            max_tokens=10,
+            messages=[{"role": "user", "content": "some blocked content"}],
+            model="anthropic/claude-3-5-sonnet-20241022",
+            custom_llm_provider="anthropic",
+            mock_response=blocked_response,
+        )
+
+    mock_base_handler.assert_not_called()
+    assert result["content"][0]["text"] == ""
+
+
 def test_presanitized_flag_not_leaked_to_provider_params():
     """The private sentinel must be popped, never forwarded as a request param."""
     from litellm.llms.anthropic.experimental_pass_through.messages import handler