How can I determine the case_value type for asset_group_listing_group_filter

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Hi,

I'm trying to find a way to determine the case_value for an asset_group_listing_group_filter. I'm using C# with the official Google Ads API client.

My query:

SELECT
    campaign.id,
    campaign.name,
    asset_group.id,
    asset_group.name,
    asset_group_listing_group_filter.id,
    asset_group_listing_group_filter.type,
    asset_group_listing_group_filter.parent_listing_group_filter
FROM asset_group_listing_group_filter
WHERE campaign.id = X

When I execute the query, my case_value property returns null. If I add case_value properties that don't exists, I'm getting an invalid argument exception. 

Should I simply try trial-and-error for every case_value type?

Cheers!