code: public Elasticsearch failureHandlerCustom(Class<? extends ActionRequestFailureHandler> failureHandlerClass) {
  		internalProperties.putString(CONNECTOR_FAILURE_HANDLER, ElasticsearchValidator.CONNECTOR_FAILURE_HANDLER_VALUE_CUSTOM);
  		internalProperties.putClass(CONNECTOR_FAILURE_HANDLER_CLASS, failureHandlerClass);
  		return this;
  	}
docs: Configures a failure handling strategy in case a request to Elasticsearch fails.
  
  <p>This strategy allows for custom failure handling using a {@link ActionRequestFailureHandler}.