@Override
    public void setParam(String key, Object value) {
        if (value == null) {
            throw new IllegalArgumentException("value cannot be null");
        }

        if (params == null) {
            params = new LinkedHashMap<>();
        }

        params.computeIfAbsent(key, k -> new ArrayList<>(3))
              .add(value.toString());
    }
Creates a new menu item without value.
primefaces/src/main/java/org/primefaces/model/menu/DefaultMenuItem.java