anchor.diff:  
         mountPoint = mkOption {
           example = "/mnt/usb";
  -        type = types.str;
  +        type = nonEmptyStr;
           description = "Location of the mounted the file system.";
         };
   
         device = mkOption {
           default = null;
           example = "/dev/sda";
  -        type = types.nullOr types.str;
  +        type = types.nullOr nonEmptyStr;
           description = "Location of the device.";
         };
   
         fsType = mkOption {
           default = "auto";
           example = "ext3";
  -        type = types.str;
  +        type = nonEmptyStr;
           description = "Type of the file system.";
         };
   
  
positive.code:       label = mkOption {
          default = null;
          example = "root-partition";
          type = types.nullOr types.str;
          description = "Label of the device (if any).";
        };
  
  
negative.code:         default = [ "defaults" ];
          example = [ "data=journal" ];
          description = "Options used to mount the file system.";
          type = types.listOf nonEmptyStr;
        };
  
      };
  