don't show empty CV topics

cv.html

@@ -9,11 +9,13 @@ redirect_from:
 or have a look at my <a href="/blog">blog</a>. Click any item for a little more detail.
 </p>
 {% for topic in site.data.cv_topics %}
+    {% assign work  = site.cv_entries | where:'type', topic.id %}
+    {% if work.size > 0 %}
     <div class = "cv-title-container">
       <h2>{{topic.name}}</h2>
       <a onClick='toggle_summary_by_class(this, "{{topic.id}}");'>Expand all</a>
     </div>
-    {% assign work  = site.cv_entries | where:'type', topic.id %}
+    
     {% for entry in work %}
       <details class="{{topic.id}}">
       <summary class="cv"><time>{{entry.period}}</time>
@@ -33,6 +35,7 @@ or have a look at my <a href="/blog">blog</a>. Click any item for a little more
       </div>
       </details>
     {% endfor %}
+    {% endif %}
 {% endfor %}