twig negate if code example

Example 1: twig if

{% if users %}
    <ul>
        {% for user in users %}
            <li>{{ user.username|e }}</li>
        {% endfor %}
    </ul>
{% endif %}

Example 2: twig if statement

{% if online == false %}
    <p>Our website is in maintenance mode. Please, come back later.</p>
{% endif %}