public void add(String key, List<String> values) {
        h.add(key, values);
    }
<p>Adds the given values to the entry of the specified key. If no entry exists for the given key, a new one is
created containing only the given values.</p>

@param key    The key with which the specified value is to be associated.
@param values The values to be added to the list associated with the specified key.
application/src/main/java/com/yahoo/application/container/handler/Headers.java