static HttpHeaders mergeDefaultHeaders(HttpHeadersBuilder lowPriorityHeaders,
                                           HttpHeaders highPriorityHeaders) {
        if (lowPriorityHeaders.isEmpty()) {
            return highPriorityHeaders;
        }

        if (highPriorityHeaders.isEmpty()) {
            return lowPriorityHeaders.build();
        }

        final HttpHeadersBuilder headersBuilder = highPriorityHeaders.toBuilder();
        for (final AsciiString name : lowPriorityHeaders.names()) {
            if (!headersBuilder.contains(name)) {
                headersBuilder.add(name, lowPriorityHeaders.getAll(name));
            }
        }
        return headersBuilder.build();
    }
Returns a newly-created {@link VirtualHost} based on the properties of this builder and the services
added to this builder.
core/src/main/java/com/linecorp/armeria/server/VirtualHostBuilder.java