anchor.diff:  
       extraCmdLineOptions = mkOption {
         description = "Extra command line options for the elasticsearch launcher.";
  -      default = [];
  +      default = [ ];
         type = types.listOf types.str;
       };
   
       extraJavaOptions = mkOption {
         description = "Extra command line options for Java.";
  -      default = [];
  +      default = [ ];
         type = types.listOf types.str;
         example = [ "-Djava.net.preferIPv4Stack=true" ];
       };
   
       plugins = mkOption {
         description = "Extra elasticsearch plugins";
  -      default = [];
  +      default = [ ];
         type = types.listOf types.package;
         example = lib.literalExample "[ pkgs.elasticsearchPlugins.discovery-ec2 ]";
       };
  
positive.code:     postBuild = "${pkgs.coreutils}/bin/mkdir -p $out/plugins";
    };
  
  in {
  
    ###### interface
  
  
negative.code:       path = [ pkgs.inetutils ];
        environment = {
          ES_HOME = cfg.dataDir;
          ES_JAVA_OPTS = toString (optional (!es6) [ "-Des.path.conf=${configDir}" ]
            ++ cfg.extraJavaOptions);
        } // optionalAttrs es6 {
          ES_PATH_CONF = configDir;
        };
  