Add the chain_cert is None case
Add the chain_cert is None case

lmcro/letsencrypt,jsha/letsencrypt,bsmr-misc-forks/letsencrypt,stweil/letsencrypt,jtl999/certbot,bsmr-misc-forks/letsencrypt,jtl999/certbot,stweil/letsencrypt,lmcro/letsencrypt,jsha/letsencrypt,letsencrypt/letsencrypt,letsencrypt/letsencrypt