Fix newsletter corruption when going back to editor from last newsletter step

assets/js/src/newsletter_editor/components/content.js

@@ -1,8 +1,9 @@
 define([
     'newsletter_editor/App',
     'backbone.supermodel',
-    'underscore'
-  ], function(App, SuperModel, _) {
+    'underscore',
+    'mailpoet'
+  ], function(App, SuperModel, _, MailPoet) {
   "use strict";
 
   var Module = {};
@@ -81,7 +82,13 @@ define([
 
   App.on('start', function(options) {
     var body = options.newsletter.body;
-    App._contentContainer = new (App.getBlockTypeModel('container'))(body.content, {parse: true});
+    var content = (_.has(body, 'content')) ? body.content : {};
+
+    if (!_.has(options.newsletter, 'body') || !_.isObject(options.newsletter.body)) {
+      MailPoet.Notice.error(MailPoet.I18n.t('newsletterBodyIsCorrupted'));
+    }
+
+    App._contentContainer = new (App.getBlockTypeModel('container'))(content, {parse: true});
     App._contentContainerView = new (App.getBlockTypeView('container'))({
       model: App._contentContainer,
       renderOptions: { depth: 0 },

assets/js/src/newsletter_editor/components/styles.js

@@ -69,11 +69,11 @@ define([
     // Expose style methods to global application
     App.getGlobalStyles = Module.getGlobalStyles;
     App.setGlobalStyles = Module.setGlobalStyles;
-
     App.getAvailableStyles = Module.getAvailableStyles;
 
     var body = options.newsletter.body;
-    this.setGlobalStyles(body.globalStyles);
+    var globalStyles = (_.has(body, 'globalStyles')) ? body.globalStyles : {};
+    this.setGlobalStyles(globalStyles);
   });
 
   App.on('start', function(options) {

assets/js/src/newsletters/send.jsx

@@ -173,15 +173,20 @@ define(
         var data = this.state.item;
         this.setState({ loading: true });
 
-        // Ensure that body is  JSON encoded
-        if (!_.isUndefined(data.body)) {
-          data.body = JSON.stringify(data.body);
-        }
+        // Store only properties that can be changed on this page
+        const IGNORED_NEWSLETTER_PROPERTIES = [
+            'preheader', 'body', 'created_at', 'deleted_at', 'hash',
+            'status', 'updated_at', 'type'
+        ];
+        const newsletterData = _.omit(
+            data,
+            IGNORED_NEWSLETTER_PROPERTIES
+        );
 
         return MailPoet.Ajax.post({
           endpoint: 'newsletters',
           action: 'save',
-          data: data,
+          data: newsletterData,
         }).always(() => {
           this.setState({ loading: false });
         });