symfony flashbag bootstrap alert

flashbag.html.twig

{% for type, messages in app.session.flashBag.all %}
    {% for message in messages %}
        {%if type == 'error'%} {% set type = 'danger' %} {%endif%}
        <div class="alert alert-{{ type }}">
            {{ message|raw }}
        </div>
    {% endfor %}
{% endfor %}