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

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