`'BaseApiClient' object has no attribute '_async_client_session_request_args'`

[sdediu00]

Environment details

• Programming language: Python
• OS: Ubuntu 24.04.3 LTS
• Language runtime version: 3.13.11
• Package version: 1.60.0

Steps to reproduce

1. Pass a custom aiohttp session to Gemini client through HttpOptions
2. Execute the following code

async def run_test() -> None:
    async with aiohttp.ClientSession() as session:
        http_options = types.HttpOptions(aiohttp_client=session)
        gemini = Client(api_key=config_lookup("GEMINI_API_KEY"), http_options=http_options)
        response = await gemini.aio.models.generate_content(
            model="gemini-2.5-flash",
            contents="What is the capital of France?",
            config=types.GenerateContentConfig(
                thinking_config=types.ThinkingConfig(thinking_budget=0),  # Disables thinking
            ),
        )
        print(response)

asyncio.run(run_test())

3. The following will get raised 'BaseApiClient' object has no attribute '_async_client_session_request_args'

I ran into this to workaround #1989 but then encountered this error

As far as I see in the code, _async_client_session_request_args never gets instantiated, leading to this error.

Not sure if I missed something that makes it possible for me to set it.

Makes it hard to use a custom aiohttp client for now.