UX: Add message when no topics found in KE view

assets/javascripts/discourse/controllers/knowledge-explorer.js.es6

@@ -44,6 +44,11 @@ export default Ember.Controller.extend({
     }
   },
 
+  @discourseComputed("topics")
+  emptyTopics(topics) {
+    return topics.length > 0 ? false : true;
+  },
+
   @discourseComputed("loadMoreUrl")
   canLoadMore(loadMoreUrl) {
     if (loadMoreUrl === null || this.isLoadingMore) {

assets/javascripts/discourse/templates/knowledge-explorer.hbs

@@ -1,4 +1,7 @@
 <div class="knowledge-explorer">
+  {{#if emptyTopics}}
+    <span class="no-topics-found">{{i18n 'knowledge_explorer.no_topics'}}</span>
+  {{else}}
     {{knowledge-explorer-search
       searchTerm=(readonly searchTerm)
       onSearch=(action "performSearch")
@@ -68,4 +71,5 @@
         {{/if}}
       </div>
     {{/conditional-loading-spinner}}
+  {{/if}}
 </div>

config/locales/client.en.yml

@@ -2,6 +2,7 @@ en:
   js:
     knowledge_explorer:
       title: "Knowledge Explorer"
+      no_topics: "No topics in Knowledge Explorer."
       categories: "Categories"
       tags: "Tags"
       search: