anchor.diff:        };
       };
   
  +  isValidLogin = login: login.username != null && login.passwordFile != null && login.registry != null;
  +
     mkService = name: container: let
       dependsOn = map (x: "${cfg.backend}-${x}.service") container.dependsOn;
     in {
  
positive.code:             will be used as the image name for docker to start a container.
            '';
            example = literalExample "pkgs.dockerTools.buildDockerImage {...};";
          };
  
          cmd = mkOption {
  
negative.code: 
      preStart = ''
        ${cfg.backend} rm -f ${name} || true
        ${optionalString (isValidLogin container.login) ''
          cat ${container.login.passwordFile} | \
            ${cfg.backend} login \
              ${container.login.registry} \
              --username ${container.login.username} \
              --password-stdin
          ''}
        ${optionalString (container.imageFile != null) ''
          ${cfg.backend} load -i ${container.imageFile}
          ''}
  