Fix #604 Chat Completion model raises runtime error when response.choices is empty (#935)

This pull request resolves #604; just checking the existence of the data and avoiding the runtime exception should make sense.

Author: seratch

src/agents/models/openai_chatcompletions.py

@@ -7,7 +7,8 @@
 
 from openai import NOT_GIVEN, AsyncOpenAI, AsyncStream
 from openai.types import ChatModel
-from openai.types.chat import ChatCompletion, ChatCompletionChunk
+from openai.types.chat import ChatCompletion, ChatCompletionChunk, ChatCompletionMessage
+from openai.types.chat.chat_completion import Choice
 from openai.types.responses import Response
 from openai.types.responses.response_prompt_param import ResponsePromptParam
 from openai.types.responses.response_usage import InputTokensDetails, OutputTokensDetails
@@ -74,8 +75,11 @@ async def get_response(
                 prompt=prompt,
             )
 
-            first_choice = response.choices[0]
-            message = first_choice.message
+            message: ChatCompletionMessage | None = None
+            first_choice: Choice | None = None
+            if response.choices and len(response.choices) > 0:
+                first_choice = response.choices[0]
+                message = first_choice.message
 
             if _debug.DONT_LOG_MODEL_DATA:
                 logger.debug("Received model response")
@@ -86,10 +90,8 @@ async def get_response(
                         json.dumps(message.model_dump(), indent=2),
                     )
                 else:
-                    logger.debug(
-                        "LLM resp had no message. finish_reason: %s",
-                        first_choice.finish_reason,
-                    )
+                    finish_reason = first_choice.finish_reason if first_choice else "-"
+                    logger.debug(f"LLM resp had no message. finish_reason: {finish_reason}")
 
             usage = (
                 Usage(