test if doi exists before linking

current-work.html

@@ -54,7 +54,12 @@ The projects in which members of our group are or have been involved are listed
     {% for project in site.data.projects %}
       <tr>
         <td>
-          <a href="https://doi.org/{{ project.grantDoi }}">{{ project.acronym }}</a> ({{ project.startDate | date: "%Y" }} - {{ project.endDate | date: "%Y" }})
+          {% if project.grantDoi %}
+            <a href="https://doi.org/{{ project.grantDoi }}">{{ project.acronym }}</a>
+          {% else %}
+            {{ project.acronym }}
+          {% endif %}
+          <br>({{ project.startDate | date: "%Y" }} - {{ project.endDate | date: "%Y" }})
         </td>
         <td class="justify">{{ project.teaser }}</td>
         <td class="nowrap">