* Even if empty string, treated as empty plainly. So "IF pmb != null" is false if empty.
     * @param hostname The parameter value of hostname. (NotNull)
     */
    public void setHostname(String hostname) {
        registerVariable("hostname", hostname);
    }

    /**
     * Set the value of count, used in parameter comment. <br>

        setupEpg(_epgMap, et -> ((FileAuthentication) et).getHostname(),
                (et, vl) -> ((FileAuthentication) et).setHostname(DfTypeUtil.toString(vl)), "hostname");
        setupEpg(_epgMap, et -> ((FileAuthentication) et).getParameters(),
                (et, vl) -> ((FileAuthentication) et).setParameters(DfTypeUtil.toString(vl)), "parameters");

                    } else {
                        postcard.addTo(fessConfig.getMailFromAddress());
                        postcard.dryrun();
                    }
                    postcard.setHostname(systemHelper.getHostname());
                    postcard.setLevel(level);
                    postcard.setCount(String.valueOf(levelEvents.size()));

                    postcard.setDataIndexSize(getValueFromMap(dataMap, "dataIndexSize", "0"));
                    postcard.setDataIndexExecTime(getValueFromMap(dataMap, "dataIndexExecTime", "0"));
                    postcard.setHostname(getValueFromMap(dataMap, "hostname", StringUtil.EMPTY));
                    postcard.setWebFsCrawlEndTime(getValueFromMap(dataMap, "webFsCrawlEndTime", StringUtil.EMPTY));