Use "no cover" img, if course not have cover

apps/course/templates/course/_items.html

@@ -7,7 +7,11 @@
     {% if course.is_deferred_start %}data-future-course data-future-course-time={{ course.deferred_start_at.timestamp }}{% endif %}
 >
 <a class="courses__preview" href="{% url 'course' course.id %}?next={{ request.get_full_path }}">
+  {% if course.cover %}
   <img class="courses__pic" src="{{ course.cover.url }}"/>
+  {% else %}
+  <img class="courses__pic" src="{% static 'img/no_cover.png' %}"/>
+  {% endif %}
   <div class="courses__view">Подробнее</div>
   {% if course.is_featured %}
   <div class="courses__label courses__label_fav"></div>