The method is currently defined as clearAuthCache({String? token}), but that appears to be a mistake from the NNBD migration; on the app-facing side, it's always called with a force-unwrapped token argument, and in the Android implementation it's required to be non-null. (I noticed this while migrating Android to Pigeon, but that behavior predates the Pigeon version).

Given that both ends are forcing it to be non-null, it's clear that this should have been {required String token} instead. We should deprecate the incorrect one, and create a new replacement with the correct nullability.