Enums in response model with no nullability or default value will make the API very fragile as each extension to the enum will break the API for some clients, but a lot of enums actually do have an unknown value which should be used as a default. This set all model properties that are non-nullable using an enum that has an Unknown member in 10.10, except MediaStream.VideoRangeType which is refactored in #13277
(cherry picked from commit 4a4fef830e)
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