public List<String> getHeadersAsList(String name) {
        List<String> values = parent.headers().get(name);
        if(values == null) {
            return List.of();
        }
        return parent.headers().get(name);
    }
Sets a header with the given name and value.
If the header had already been set, the new value overwrites the previous one.
container-core/src/main/java/com/yahoo/jdisc/http/filter/DiscFilterRequest.java