anchor.diff:          default = [ "defaults" ];
           example = [ "data=journal" ];
           description = "Options used to mount the file system.";
  -        type = types.listOf types.str;
  +        type = types.listOf nonEmptyStr;
         };
   
       };
  
positive.code:       label = mkOption {
          default = null;
          example = "root-partition";
          type = types.nullOr types.str;
          description = "Label of the device (if any).";
        };
  
  
negative.code: with utils;
  
  let
  
    addCheckDesc = desc: elemType: check: types.addCheck elemType check
      // { description = "${elemType.description} (with check: ${desc})"; };
    nonEmptyStr = addCheckDesc "non-empty" types.str
      (x: x != "" && ! (all (c: c == " " || c == "\t") (stringToCharacters x)));
  
    fileSystems' = toposort fsBefore (attrValues config.fileSystems);
  
  