Currently, if the ID is invalid, parentKey is set to null, causing it to return all history entries. Note that there is still a problem that you cannot look up history entries for entities which have been soft deleted, because the foreign key lookup won't work. That is unfortunate, but at least this simple fix makes things better than they were.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=154564262