static Http1HeaderNaming traditional() {
        return headerName -> {
            final String originalHeaderName = HttpHeaderNames.rawHeaderName(headerName);
            return firstNonNull(originalHeaderName, headerName.toString());
        };
    }
Converts lower-cased HTTP/2 header names to the traditional HTTP/1 header names which are defined at
{@link HttpHeaderNames}. For example, {@code "user-agent"} is converted to {@code "User-Agent"}.
Note that a header name which is not defined at {@link HttpHeaderNames} will be sent in lower-case.
core/src/main/java/com/linecorp/armeria/common/Http1HeaderNaming.java