Ping fails due to NullReferenceException after upgrading

[VMelnalksnis]

Elastic.Clients.Elasticsearch version: 8.1.1

Elasticsearch version: 8.6.1

.NET runtime version: 6.0

Operating system version: Windows 10 22H2

Description of the problem including expected versus actual behavior:
After upgrading to the new client, Ping method fails either with previous or minimal configuration.
While debugging I tracked it down to this line in HttpTransportClient method public override TResponse Request<TResponse>(RequestData requestData):

mimeType = responseMessage.Content.Headers.ContentType.ToString();

The exception is thrown because the response content does not have any headers.

Steps to reproduce:

1. Create new ElasticsearchClient with the settings below
2. Call ElasticsearchClient.Ping()
3. See UnexpectedTransportException with inner NullReferenceException

Expected behavior
Ping succeeds.

Provide ConnectionSettings (if relevant):

new ElasticsearchClientSettings(Uri)
    .Authentication(new BasicAuthentication(userName, password));

[stevejgordon]

This has recently been fixed in elastic/elastic-transport-net#78, and we will need to update to the latest patch to pick up this fix. @VMelnalksnis In the mean time, as this only affected the sync path, PingAsync should work for you and would be recommended as best practice.

[VMelnalksnis]

Thanks, I was using the sync version to check the connection on creation instead of first use, but I'll check if it's possible to convert it to async.