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
By moving []s into the batch package, which is not included in the frontend service, we pave the way to remove the dependency of frontend on the [] library.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=142265351