Explicitly define value for likert-row

projects/common/models/elements/compound-elements/likert/likert-row.ts

@@ -13,6 +13,7 @@ import { InstantiationEror } from 'common/util/errors';
 
 export class LikertRowElement extends InputElement implements LikertRowProperties {
   type: UIElementType = 'likert-row';
+  value: number | null = null;
   rowLabel: TextImageLabel = { text: '', imgSrc: null, imgPosition: 'above' };
   columnCount: number = 0;
   firstColumnSizeRatio: number = 5;