Keep storage.names() from passing None to open()
Keep storage.names() from passing None to open()

Fixes exiting abnormally with:
    TypeError: coercing to Unicode: need string or buffer, NoneType found

thanatos/lets-encrypt-preview,jtl999/certbot,letsencrypt/letsencrypt,mitnk/letsencrypt,wteiken/letsencrypt,mitnk/letsencrypt,jtl999/certbot,brentdax/letsencrypt,stweil/letsencrypt,kuba/letsencrypt,thanatos/lets-encrypt-preview,TheBoegl/letsencrypt,VladimirTyrin/letsencrypt,jsha/letsencrypt,lmcro/letsencrypt,DavidGarciaCat/letsencrypt,twstrike/le_for_patching,DavidGarciaCat/letsencrypt,dietsche/letsencrypt,letsencrypt/letsencrypt,kuba/letsencrypt,brentdax/letsencrypt,bsmr-misc-forks/letsencrypt,twstrike/le_for_patching,dietsche/letsencrypt,lmcro/letsencrypt,bsmr-misc-forks/letsencrypt,jsha/letsencrypt,stweil/letsencrypt,VladimirTyrin/letsencrypt,wteiken/letsencrypt,TheBoegl/letsencrypt