@Override
        @Nullable
        public String header(String name) {
            final HttpRequest req = ctx.request();
            return req != null ? req.headers().get(name) : null;
        }
Wraps a pair of {@link ClientRequestContext} and {@link RequestHeadersBuilder} in an {@link
brave.http.HttpClientRequest}.
brave/brave6/src/main/java/com/linecorp/armeria/client/brave/ClientRequestContextAdapter.java