Query Index with dynamic template mapping not working at all

[matthewyang0807]

Elastic.Clients.Elasticsearch version:8.0.5

Elasticsearch version:8.0

.NET runtime version:6.0

Operating system version:Win11

Description of the problem including expected versus actual behavior:
A clear and concise description of what the bug is.

Steps to reproduce:

1. Create a simple index only has dynamic template mapping like this:
   

2. then use console to write a simple query like this:
   var es8client = GetES8();
   GetIndexRequest cr = new GetIndexRequest("matthew_simple_dynamictemplateindex");
   var response = es8client.Indices.GetAsync(cr);
   Console.WriteLine(response.Result.ApiCallDetails.HasSuccessfulStatusCode);
   Console.WriteLine(response.Result.ApiCallDetails.HttpStatusCode);

3. The error will come out:

Expected behavior
A clear and concise description of what you expected to happen.
I would expect this query can be successful with no error.

[stevejgordon]

Closing as a duplicate of #7221.