Without specific notice, ProGuard will lop off readObject, readResolve, etc.,
which can lead to baffling failures, even when just serializing library
classes. For example, if you're serializing Scala Option[T] objects, losing
readResolve can get you duplicates of None, which is ordinarily a singleton;
that, in turn, can lead to spurious, and very strange-looking MatchExceptions.