[CSHARP] Duplicate headers causing exception

When returning the ApiResponse, the method ToDictionary is used to construct a response object from a raw API response. The method ToDictionary will expect only unique keys, but this is not always the case. For example, headers could repeat which would cause the code to end in an exception.

Here is an example from the generated code:

            return new ApiResponse<KeycloakTokenResponse>(localVarStatusCode,
                localVarResponse.Headers.ToDictionary(x => x.Name, x => string.Join(",", x.Value)),
                (KeycloakTokenResponse) this.Configuration.ApiClient.Deserialize(localVarResponse, typeof(KeycloakTokenResponse)));
nResponse) this.Configuration.ApiClient.Deserialize(localVarResponse, typeof(KeycloakTokenResponse)));

and here is the modification I had to make:

            return new ApiResponse<KeycloakTokenResponse>(localVarStatusCode,
                localVarResponse.Headers.GroupBy(x => x.Name)
                    .ToDictionary(g => g.Key, g => g.Select(x => x.Value).ToString()),
                (KeycloakTokenResponse) this.Configuration.ApiClient.Deserialize(localVarResponse, typeof(KeycloakTokenResponse)));

This workaround means that duplicates are allowed in the response headers. I believe this should be part of the generated code, but I am asking for any contrasting opinion.

Start at the generated C# ApiResponse construction using localVarResponse.Headers.ToDictionary, and trace how this output is produced. Verify the generated response-header handling with repeated header names, ensuring the response no longer fails because of duplicate keys; the issue does not name a source file or test to run.