🐛 Fixed error rendering count with no number (#13)

refs https://github.com/TryGhost/Team/issues/2221

- added guard to `formatNumber` helper used in the `<Count>` component via the `<ContentTitle>` component so a missing count prop is handled gracefully

apps/comments-ui/src/utils/helpers.js

@@ -23,6 +23,10 @@ export function isSentryEventAllowed({event: sentryEvent}) {
 }
 
 export function formatNumber(number) {
+    if (number !== 0 && !number) {
+        return '';
+    }
+
     // Adds in commas for separators
     return number.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ',');
 }

apps/comments-ui/src/utils/helpers.test.js

@@ -0,0 +1,19 @@
+import * as helpers from './helpers';
+
+describe('formatNumber', function () {
+    it('adds commas to large numbers', function () {
+        expect(helpers.formatNumber(1234567)).toEqual('1,234,567');
+    });
+
+    it('handles 0', function () {
+        expect(helpers.formatNumber(0)).toEqual('0');
+    });
+
+    it('handles undefined', function () {
+        expect(helpers.formatNumber()).toEqual('');
+    });
+
+    it('handles null', function () {
+        expect(helpers.formatNumber(null)).toEqual('');
+    });
+});