Handled null sources for attribution chart and table

refs https://github.com/TryGhost/Team/issues/1932

- removes null sources from attribution chart
- moves null sources count to bottom of attribution table

ghost/admin/app/components/dashboard/charts/attribution.hbs

@@ -10,7 +10,7 @@
 
             <div style="border-left: 1px solid #eceef0; padding-left: 48px;display: flex;justify-content: center;align-items: center;">
                 <div style="max-width: 200px;">
-                    <MemberAttribution::SourceAttributionChart @sources={{this.sources}} />
+                    <MemberAttribution::SourceAttributionChart @sources={{this.chartSources}} />
                 </div>
             </div>
         </div>

ghost/admin/app/components/dashboard/charts/attribution.js

@@ -14,6 +14,12 @@ export default class Recents extends Component {
         return this.dashboardStats?.memberSourceAttributionCounts || [];
     }
 
+    get chartSources() {
+        const counts = this.dashboardStats?.memberSourceAttributionCounts || [];
+        // filter null source from the list
+        return counts.filter(source => source.source);
+    }
+
     get areMembersEnabled() {
         return this.dashboardStats.siteStatus?.membersEnabled;
     }

ghost/admin/app/components/member-attribution/source-attribution-table.hbs

@@ -7,7 +7,7 @@
         {{/if}}
     </div>
     <div class="gh-dashboard-list-body">
-        {{#each @sources as |sourceData|}}
+        {{#each this.sources as |sourceData|}}
             <div class="gh-dashboard-list-item">
                 <div class="gh-dashboard-list-item-sub">
                     <span class="gh-dashboard-list-text">{{sourceData.source}}</span>

ghost/admin/app/components/member-attribution/source-attribution-table.js

@@ -3,4 +3,18 @@ import {inject as service} from '@ember/service';
 
 export default class SourceAttributionTable extends Component {
     @service membersUtils;
+
+    get sources() {
+        const availableSources = this.args.sources.filter(source => source.source);
+        const unavailableSources = this.args.sources.filter(sourceData => !sourceData.source).map((sourceData) => {
+            return {
+                ...sourceData,
+                source: 'Unavailable'
+            };
+        });
+        return [
+            ...availableSources,
+            ...unavailableSources
+        ];
+    }
 }