GenerateContentConfig.media_resolution = None leads to degraded vision performance

Applies for gemini-2.5 onwards: When I use GenerateContentConfig.media_resolution = None , vision performance is negatively impacted.
If I instead set it explicitly to types.MediaResolution.MEDIA_RESOLUTION_UNSPECIFIED, performance is good as usual. I found this by chance due to a refactor.

Our team internal bench suite shows a ~10% performance drop when using None; it's a 2-field data extraction task from ~1080p images.

Weird part is that token usage is the same as using MEDIA_RESOLUTION_UNSPECIFIED.

I didn't find any documentation showing the difference between None and MEDIA_RESOLUTION_UNSPECIFIED enum, so I always assumed they would be the same. They are not, apparently..?

At this point I've already solved the problem, but I'd like to have an explanation from someone that knows the internals.. out of curiosity. If hope that the media res enum has a good reason to be Optional and not default to MEDIA_RESOLUTION_UNSPECIFIED.
Plus, I hope this may help other people.

`google.genai version == 1.57.0`, `python 3.10.8`