I should have caught this in the review, but [] is loading *ALL*
contacts individually from Datastore on every domain update. This will add a
large number of Datastore round trips and thus significantly reduce update
performance.
This CL changes the behavior to *ONLY* load contacts when there is a duplicate
(which is needed to determine the contact's display name to generate the error
message), and loads all of them in a single batch rather than individually.
This also makes some minor changes around domain getters returning empty sets
instead of null.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=233128140
49ac4e3e69