message: adjusted for strick mode
diff: @@ -6,9 +6,8 @@ import { Sort } from '../sort';
  export interface JsonEntityStorage {
  - getItem(entityDbName: string): string;
  + getItem(entityDbName: string): string | null;
  setItem(entityDbName: string, json: string);
  -
  }
  export class JsonDataProvider implements DataProvider {
  