fix an unknown NPE in the frontend

Author: David Blackman

docs/compare.html

@@ -602,8 +602,8 @@ <h5 class="card-title" id="summary-{{key}}">{{key}}</h5>
               index: index + 1,
               total: changes.length,
               params: JSON.stringify(change.query.params, null, 2),
-              oldUrl: change.old.url,
-              newUrl: change.new.url,
+              oldUrl: change.old?.url,
+              newUrl: change.new?.url,
               oldHost: json.old.apiEnv.host,
               newHost: json.new.apiEnv.host,
               id: change.id,