Usage of addHeader method on the WebClient.Builder duplicates headers

[Verdent]

Use method addHeader on the WebClient.Builder, create WebClient and perfom any request on this client. All registered headers over the WebClient.Builder are duplicated.

WebClient.builder()
            .baseUri(someUri)
            .addHeader("TestHeader", "Value")
            .build()
            .get("/someEndpoint")
            .request();

If headers are registered directly to the request builder, it works without duplication.