NullReferenceException when disposing of ConnectionSettings

[reduckted]

NEST/Elasticsearch.Net version:

• NEST v7.8.0
• Elasticsearch.Net v7.8.0

Elasticsearch version:
N/A

Description of the problem including expected versus actual behavior:

Disposing of a Nest.ConnectionSettings object that has not been used throws a NullReferenceException.

Steps to reproduce:
Simply run this code in a .NET Core project (didn't seem to happen with a .NET Framework project):

using (var settings = new ConnectionSettings())
{
}

System.NullReferenceException: 'Object reference not set to an instance of an object.'
   at Elasticsearch.Net.RequestDataHttpClientFactory.StopCleanupTimer()
   at Elasticsearch.Net.RequestDataHttpClientFactory.CleanupTimer_Tick()
   at Elasticsearch.Net.RequestDataHttpClientFactory.Dispose()
   at Elasticsearch.Net.HttpConnection.DisposeManagedResources()
   at Elasticsearch.Net.HttpConnection.System.IDisposable.Dispose()
   at Elasticsearch.Net.ConnectionConfiguration`1.DisposeManagedResources()
   at Elasticsearch.Net.ConnectionConfiguration`1.System.IDisposable.Dispose()

Expected behavior
An exception is not thrown.

Provide ConnectionSettings (if relevant):
N/A

Provide DebugInformation (if relevant):
N/A

[jdaltonchilders]

Downgrading to Elasticsearch.Net and NEST version 7.7.1 resolve the error on .Net Core 3.1.

[russcam]

Thanks for opening @reduckted. This is related to the internal HttpClientFactory introduced to refresh clients in 7.8.0. We'll look to fix this.