This was a surprisingly involved change. Some of the difficulties included
java.util.Optional purposely not being Serializable (so I had to move a
few Optionals in mapreduce classes to @Nullable) and having to add the Truth
Java8 extension library for assertion support.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171863777
Also had to add an EnumParameter class to support
List<T extends Enum<T>>, as these aren't natively supported by
JCommander (although single Enum parameters are.)
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=129464699