fix MongoDB custom Key type
fix MongoDB custom Key type

paul-rouse/persistent,mitchellwrosen/persistent,jasonzoladz/persistent,creichert/persistent,greydot/persistent,naushadh/persistent,junjihashimoto/persistent,gbwey/persistent,jcristovao/persistent,greydot/persistent,meteficha/persistent,jasonzoladz/persistent,jcristovao/persistent,nakaji-dayo/persistent,gbwey/persistent,mkscrg/persistent,erikd/persistent,mkscrg/persistent,mitchellwrosen/persistent,pseudonom/persistent,superduper/persistent,psibi/persistent,jasonzoladz/persistent,mitchellwrosen/persistent,plow-technologies/persistent,meteficha/persistent,nakaji-dayo/persistent,andrewthad/persistent,yesodweb/persistent,andrewthad/persistent,rdnetto/persistent,gbwey/persistent,meteficha/persistent,jcristovao/persistent,greydot/persistent,junjihashimoto/persistent,superduper/persistent,superduper/persistent,mkscrg/persistent,nakaji-dayo/persistent,rdnetto/persistent,pseudonom/persistent,andrewthad/persistent,bitemyapp/persistent