Crashed when bulk write in high concurrency

when bulk write in high concurrency, sometimes I got stacktrace like:

 2020-06-29 16:04:50.735 ERROR xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    java.lang.NullPointerException: null
            at org.elasticsearch.client.RequestLogger.logResponse(RequestLogger.java:60) ~[elasticsearch-rest-client-7.6.2.jar:7.6.2]
            at org.elasticsearch.client.RestClient.convertResponse(RestClient.java:273) ~[elasticsearch-rest-client-7.6.2.jar:7.6.2]
            at org.elasticsearch.client.RestClient.performRequest(RestClient.java:261) ~[elasticsearch-rest-client-7.6.2.jar:7.6.2]
            at org.elasticsearch.client.RestClient.performRequest(RestClient.java:235) ~[elasticsearch-rest-client-7.6.2.jar:7.6.2]
            at org.elasticsearch.client.RestHighLevelClient.internalPerformRequest(RestHighLevelClient.java:1514) ~[elasticsearch-rest-high-level-client-7.6.2.jar:7.6.2]
            at org.elasticsearch.client.RestHighLevelClient.performRequest(RestHighLevelClient.java:1484) ~[elasticsearch-rest-high-level-client-7.6.2.jar:7.6.2]
            at org.elasticsearch.client.RestHighLevelClient.performRequestAndParseEntity(RestHighLevelClient.java:1454) ~[elasticsearch-rest-high-level-client-7.6.2.jar:7.6.2]
            at org.elasticsearch.client.RestHighLevelClient.bulk(RestHighLevelClient.java:497) ~[elasticsearch-rest-high-level-client-7.6.2.jar:7.6.2]
            at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
            at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
            at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
            at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
            at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
            at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
            at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1626) [?:1.8.0_191]
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_191]
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_191]
            at java.lang.Thread.run(Thread.java:748) [?:1.8.0_191]

when crashed multi times, it will throw another exception like:
java.lang.RuntimeException: I/O reactor

follow the code I found in this function:

     private Response performRequest(final NodeTuple<Iterator<Node>> nodeTuple,
                                    final InternalRequest request,
                                    Exception previousException) throws IOException {
        RequestContext context = request.createContextForNextAttempt(nodeTuple.nodes.next(), nodeTuple.authCache);
        HttpResponse httpResponse;
        try {
            httpResponse = client.execute(context.requestProducer, context.asyncResponseConsumer, context.context, null).get();
        } catch(Exception e) {
            RequestLogger.logFailedRequest(logger, request.httpRequest, context.node, e);
            onFailure(context.node);
            Exception cause = extractAndWrapCause(e);
            addSuppressedException(previousException, cause);
            if (nodeTuple.nodes.hasNext()) {
                return performRequest(nodeTuple, request, cause);
            }
            if (cause instanceof IOException) {
                throw (IOException) cause;
            }
            if (cause instanceof RuntimeException) {
                throw (RuntimeException) cause;
            }
            throw new IllegalStateException("unexpected exception type: must be either RuntimeException or IOException", cause);
        }
        ResponseOrResponseException responseOrResponseException = convertResponse(request, context.node, httpResponse);
        if (responseOrResponseException.responseException == null) {
            return responseOrResponseException.response;
        }
        addSuppressedException(previousException, responseOrResponseException.responseException);
        if (nodeTuple.nodes.hasNext()) {
            return performRequest(nodeTuple, request, responseOrResponseException.responseException);
        }
        throw responseOrResponseException.responseException;
    }

maybe client.execute return null result