Description of the bug:

The function_call type is not handled at all in this function (and raises an exception, which might be expected but is a bit counter intuitive):
https://github.com/google-gemini/generative-ai-python/blob/v0.8.4/google/generativeai/types/generation_types.py#L512-L536

Further more this line (that deals with the missing case), has a type and should be WhichOneOf instead of whichOneOf.
https://github.com/google-gemini/generative-ai-python/blob/v0.8.4/google/generativeai/types/generation_types.py#L535-L536

Is there a reason for .text to raise an exception when the result only contains a function call

Actual vs expected behavior:

No response

Any other information you'd like to share?

No response