Do you still want me to add the same checks to HarbormasterBuildUnitMessage->newFromDictionary()? AFAICT, that would just move the error message from save time to creation time.

Also, I landed this onto experimental. Do we want this on master as well? If so, what's the best way to accomplish that? arc land --revision D18603 --onto master?

newFromDictionary() gets called before saving the records in the database (JSON is converted to objects with newFromDictionary(), then saved). It's maybe worth doing since it'll be a slightly nicer experience for old arc clients or manual Conduit callers, but not a big deal either way.

Easiest is probably git cherry-pick <commit> + git push, land doesn't know that you want to cherry-pick instead of rebase/merge.