one.twig

<a href="{% route 'product_sellable' with ["sellerName":  activity.sellable.seller.identity.username , "productSlug": activity.sellable.product.slug] %}">
	<img src="{{ activity.sellable.product.images[0].thumbUrl }}">
</a>

two.twig

{% if activity.sellable %}
	{% if activity.sellable.seller %}
		{% if activity.sellable.seller.identity %}
			{% if activity.sellable.seller.identity.username %}
				{% if activity.sellable %}
					{% if activity.sellable.product %}
						{% if activity.sellable.product.slug %}
							<a href="{% route 'product_sellable' with ["sellerName":  activity.sellable.seller.identity.username , "productSlug": activity.sellable.product.slug] %}">
								{% if activity.sellable %}
									{% if activity.sellable.product %}
										{% if count(activity.sellable.product.images) > 0 %}
											{% if count(activity.sellable.product.images[0].thumbUrl %}
												<img src="{{ activity.sellable.product.images[0].thumbUrl }}">
											{% endif %}
										{% endif %}
									{% endif %}
								{% endif %}
							</a>
						{% endif %}
					{% endif %}
				{% endif %}
			{% endif %}
		{% endif %}
	{% endif %}
{% endif %}