Don't output tags partial if there are no tags

layouts/partials/tags.html

@@ -1,5 +1,7 @@
+{{ if .Params.tags }}
 <ul class="tags">
   {{ range sort .Params.tags }}
   <li><a href="{{ relURL "/tags/" }}{{ . | urlize }}/">{{ . }}</a></li>
   {{ end }}
 </ul>
+{{ end }}