code: protected String getBulkData(List<SimpleDataEvent> events) {
      StringBuilder builder = new StringBuilder();
      for (SimpleDataEvent event : events) {
        builder.append(JSONUtils.getElasticSearchBulkHeader(event, this.indexName, this.typeName));
        builder.append("\n");
        builder.append(JSONUtils.getElasticSearchAddDocument(event.pairs()));
        builder.append("\n");
      }
      return builder.toString();
    }
docs: Returns ES bulk data.
  
  @return ES bulk data