*
    * @param searchLogEvent The search log event.
    * @return The source map.
    */
    protected Map<String, Object> toSource(final SearchLogEvent searchLogEvent) {
        final Map<String, Object> source = toLowerHyphen(searchLogEvent.toSource());
        source.put("_id", searchLogEvent.getId());
        // source.put("version_no", searchLogEvent.getVersionNo());
        source.put("event_type", searchLogEvent.getEventType());