Handle empty array of slack setting objects

no issue
- ensure at least one SlackIntegration object exists in the slack setting when deserialising
- remove blank SlackIntegration objects when serialising

ghost/admin/app/transforms/slack-settings.js

@@ -1,19 +1,25 @@
 /* eslint-disable camelcase */
 import SlackObject from 'ghost-admin/models/slack-integration';
 import Transform from 'ember-data/transform';
-import {A as emberA, isArray as isEmberArray} from '@ember/array';
+import {isArray as isEmberArray} from '@ember/array';
+import {isEmpty} from '@ember/utils';
 
 export default Transform.extend({
     deserialize(serialized) {
-        let slackObj, settingsArray;
+        let settingsArray;
         try {
             settingsArray = JSON.parse(serialized) || [];
         } catch (e) {
             settingsArray = [];
         }
 
-        slackObj = settingsArray.map(itemDetails => SlackObject.create(itemDetails));
-        return emberA(slackObj);
+        if (isEmpty(settingsArray)) {
+            settingsArray.push({url: ''});
+        }
+
+        let slackObjs = settingsArray.map(itemDetails => SlackObject.create(itemDetails));
+
+        return slackObjs;
     },
 
     serialize(deserialized) {
@@ -21,8 +27,9 @@ export default Transform.extend({
         if (isEmberArray(deserialized)) {
             settingsArray = deserialized.map((item) => {
                 let url = (item.get('url') || '').trim();
-
-                return {url};
+                if (url) {
+                    return {url};
+                }
             }).compact();
         } else {
             settingsArray = [];

ghost/admin/tests/unit/transforms/slack-settings-test.js

@@ -6,6 +6,7 @@ import {setupTest} from 'ember-mocha';
 
 describe('Unit: Transform: slack-settings', function () {
     setupTest('transform:slack-settings', {});
+
     it('deserializes settings json', function () {
         let transform = this.subject();
         let serialized = '[{"url":"http://myblog.com/blogpost1"}]';
@@ -16,6 +17,16 @@ describe('Unit: Transform: slack-settings', function () {
         expect(result[0].get('url')).to.equal('http://myblog.com/blogpost1');
     });
 
+    it('deserializes empty array', function () {
+        let transform = this.subject();
+        let serialized = '[]';
+        let result = transform.deserialize(serialized);
+
+        expect(result.length).to.equal(1);
+        expect(result[0]).to.be.instanceof(SlackIntegration);
+        expect(result[0].get('url')).to.equal('');
+    });
+
     it('serializes array of Slack settings', function () {
         let transform = this.subject();
         let deserialized = emberA([
@@ -25,4 +36,14 @@ describe('Unit: Transform: slack-settings', function () {
 
         expect(result).to.equal('[{"url":"http://myblog.com/blogpost1"}]');
     });
+
+    it('serializes empty SlackIntegration objects', function () {
+        let transform = this.subject();
+        let deserialized = emberA([
+            SlackIntegration.create({url: ''})
+        ]);
+        let result = transform.serialize(deserialized);
+
+        expect(result).to.equal('[]');
+    });
 });