How to use the bunyan.default.createLogger function in bunyan

if (process.env.GTM_LOGSTASH_HOST) {
        let logstashPort = process.env.GTM_LOGSTASH_PORT || 5000;

        bunyanConf.streams.push({
            type: 'raw',
            stream: bunyanTcp
                .createStream({
                    host: process.env.GTM_LOGSTASH_HOST,
                    port: logstashPort
                })
                .on('error', console.error)
        });
    }

    return bunyan.createLogger(bunyanConf);
}