Change CheckAndSet a bit.
Change CheckAndSet a bit.

Empty starting oldValue is now equivalent to Create.

alexdebrie/pachyderm,alexdebrie/pachyderm,klucar/pachyderm,sambooo/pachyderm,kunthar/pachyderm,ShengjieLuo/pachyderm,sambooo/pachyderm,ShengjieLuo/pachyderm,klucar/pachyderm,phacops/pachyderm,ShengjieLuo/pachyderm,phacops/pachyderm,alexdebrie/pachyderm,kunthar/pachyderm,sambooo/pachyderm,klucar/pachyderm