make toArray_ param non-null
make toArray_ param non-null

RELNOTES: n/a No public API change.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=228981489

lucidsoftware/closure-library,google/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library,google/closure-library,google/closure-library,google/closure-library,lucidsoftware/closure-library,google/closure-library