{% if product.imagesByType('thumbnail') is not empty %}
    {% set path = product.imagesByType('thumbnail').first.path|imagine_filter(filter|default('sylius_admin_product_thumbnail')) %}
{% elseif product.images.first %}
    {% set path = product.images.first.path|imagine_filter(filter|default('sylius_admin_product_thumbnail')) %}
{% else %}
    {% set path = '//placehold.it/50x50' %}
{% endif %}

<img src="{{ path }}" alt="" class="ui bordered image sylius-grid-image" />
