The default of an optional constant should be None

[Juliehzl]

For an optional enum type with only one item, we will expect the default value is None not non-None value.
Because with a non-None value, it will change the operation behavior, which is breaking change to customer.

modelAsString to true could resolve the issue, but adding such change will cause breaking change to .Net SDK.
So we will hope python generator could fix the issue asap.

[iscai-msft]

@Juliehzl seems the swagger has already been fixed, so you should be unblocked by the swagger fix.

This is still a valid scenario that autorest wants to fix, so your issue is still valuable and I will work on implementing this. Thanks @Juliehzl !

[iscai-msft]

Add flag --legacy-default. This will be tied to the version-intolerant generation of autorest. With --legacy-default, we'll default optional constants to their one possible non-None value. We think this is a design issue, and want to fix this in a non breaking way to default to None (unless they've specified x-ms-client-default