Fix display bug

submissions/templates/partials/submissions/submission_card_content.html

@@ -5,7 +5,7 @@
         Version {{ submission.preprint.vn_nr }} ({% if submission.is_current %}current version{% else %}deprecated version {{ submission.preprint.vn_nr }}{% endif %})
         <br>
         {% if submission.publication and submission.publication.is_published %}
-            Published as <a href="{{ submission.publication.get_absolute_url }}">{{ submission.publication.in_issue.in_volume.in_journal.abbreviation_citation }} <strong>{{ submission.publication.in_issue.in_volume.number }}</strong>, {{ submission.publication.get_paper_nr }} ({{ submission.publication.publication_date|date:'Y' }})</a>
+            Published as <a href="{{ submission.publication.get_absolute_url }}">{{ submission.publication.get_journal.abbreviation_citation }}{% if submission.publication.in_issue.in_volume %} <strong>{{ submission.publication.in_issue.in_volume.number }}</strong>,{% endif %} {{ submission.publication.get_paper_nr }} ({{ submission.publication.publication_date|date:'Y' }})</a>
         {% else %}
             Submitted {{ submission.submission_date }} to {{ submission.get_submitted_to_journal_display }}
         {% endif %} &middot; latest activity: {{ submission.latest_activity }}