Volt: is partial exists

Is it possible to check if partial exists?

Something like

<div id="footer">
    {% if is_file("footer") %}
        {{ partial("footer") }}
    {% else %}
        Partial "footer" doesn't exists
    {% endif %}
</div>

Not with the built-in functions I think. However, if it's necessary for you, you can add a helper function, see http://docs.phalconphp.com/en/latest/reference/volt.html#id3