@Override
	public void add(IndexRequest... indexRequests) {
		for (IndexRequest indexRequest : indexRequests) {
			if (flushOnCheckpoint) {
				numPendingRequestsRef.getAndIncrement();
			}
			this.bulkProcessor.add(indexRequest);
		}
	}
Implementation of a {@link RequestIndexer}, using a {@link BulkProcessor}.
{@link ActionRequest ActionRequests} will be buffered before sending a bulk request to the Elasticsearch cluster.

@deprecated This class is not binary compatible with newer Elasticsearch 6+ versions
            (i.e. the {@link #add(UpdateRequest...)} ). However, this module is currently
            compiled against a very old Elasticsearch version.
elasticsearch5-xh/elasticsearch5-xh-sink/src/main/java/org/apache/flink/streaming/connectors/elasticsearch/PreElasticsearch6BulkProcessorIndexer.java