Fixed fromDTO collection mapping

refs https://github.com/TryGhost/Team/issues/3260

- Whenever properties of the DTO are undefined they should be removed to avoid unintentional empty assignments to the stored collection

ghost/collections/src/CollectionsService.ts

@@ -74,13 +74,22 @@ export class CollectionsService {
     }
 
     fromDTO(data: any): any {
-        return {
+        const mappedDTO: {[index: string]:any} = {
             title: data.title,
             slug: data.slug,
             description: data.description,
             featureImage: data.feature_image,
             filter: data.filter
         };
+
+        // delete out keys that contain undefined values
+        for (const key of Object.keys(mappedDTO)) {
+            if (mappedDTO[key] === undefined) {
+                delete mappedDTO[key];
+            }
+        }
+
+        return mappedDTO;
     }
 
     async createCollection(data: CollectionInputDTO): Promise<CollectionDTO> {

ghost/collections/test/collections.test.ts

@@ -1,5 +1,5 @@
 import assert from 'assert';
-import {CollectionsService, CollectionsRepositoryInMemory} from '../src/index';
+import {CollectionsService, CollectionsRepositoryInMemory, Collection} from '../src/index';
 import {posts} from './fixtures/posts';
 
 describe('CollectionsService', function () {
@@ -40,6 +40,16 @@ describe('CollectionsService', function () {
         assert.equal(deletedCollection, null, 'Collection should be deleted');
     });
 
+    describe('toDTO', function () {
+        it('Can map Collection entity to DTO object', async function () {
+            const collection = await Collection.create({});
+            const dto = collectionsService.toDTO(collection);
+
+            assert.equal(dto.id, collection.id, 'DTO should have the same id as the entity');
+            assert.equal(dto.title, null, 'DTO should return null if nullable property of the entity is unassigned');
+        });
+    });
+
     describe('addPostToCollection', function () {
         it('Can add a Post to a Collection', async function () {
             const collection = await collectionsService.createCollection({