Make tracked_refs optional

If an edition has a tracked_refs key of None, then the GitHub link is
simply not shown.

An edition can have tracked_refs = None because it uses an alternative
tracking mode.

Also switch to using the edition's `slug` field instead of the
`git_refs` because the slug should always be present.

app/dashboard/render.py

@@ -168,7 +168,14 @@ def _insert_github_ref_url(product, edition_dataset,
     """
     base_repo_url = product['doc_repo'].rstrip('.git')
     for k, d in edition_dataset.items():
-        git_ref = d[git_refs_key][0]
+        # Editions that don't use the git_refs tracking mode will have
+        # tracked_refs equal to None.
+        try:
+            git_ref = d[git_refs_key][0]
+        except TypeError:
+            # None is not indexable
+            continue
+
         # https://github.com/lsst-sqre/ltd-dasher/tree/tickets/DM-9023
         url = base_repo_url + '/tree/' + git_ref
         d[key] = url
@@ -182,7 +189,14 @@ def _insert_jira_url(edition_dataset, git_refs_key='tracked_refs',
     re-thought for multi-repo LTD products.
     """
     for k, d in edition_dataset.items():
-        git_ref = d[git_refs_key][0]
+        # Editions that don't use the git_refs tracking mode will have
+        # tracked_refs equal to None.
+        try:
+            git_ref = d[git_refs_key][0]
+        except TypeError:
+            # None is not indexable
+            continue
+
         match = TICKET_BRANCH_PATTERN.search(git_ref)
         if match is not None:
             ticket_name = match.group(1)
@@ -251,11 +265,11 @@ def _insert_is_release(editions,
     Heuristic for guessing a release: edition slug begins with `v` and a digit.
     """
     for k, d in editions.items():
-        git_ref = d['tracked_refs'][0]
-        match = RELEASE_PATTERN.search(git_ref)
+        slug = d['slug']
+        match = RELEASE_PATTERN.search(slug)
         if match is not None:
             d[is_release_key] = True
-            d[alt_title_key] = git_ref
+            d[alt_title_key] = slug
         else:
             d[is_release_key] = False
 

app/dashboard/templates/_edition_item.jinja

@@ -28,10 +28,12 @@
         <span><span class="svg-icon svg-icon--left svg-icon--jira svg-baseline"><svg><use xlink:href="#icon-jira-blue" /></svg></span> <a href="{{ item.jira_url }}">{{ item.jira_ticket_name }}</a></span>
       </div>
     {% endif %}
+    {% if item.github_ref_url %}
     <div class="inventory-item-metadata__github-branch-box">
       {# FIXME could have an edition with multiple branches (multi-repo products)
       For the MVP I'm ignoring this. #}
       <span><span class="svg-icon svg-icon--left svg-baseline"><svg><use xlink:href="#octicon-mark-github" /></svg></span><a href="{{ item.github_ref_url }}">View source</a></span>
     </div>
+    {% endif %}
   </div>
 </article>