message: Improve mock localStorage
diff: let _localStorage = {};
  (window as any).localStorage = (window as any).sessionStorage = {
  - setItem(key, value) {
  + setItem(key: string, value: string) {
  Object.assign(_localStorage, { [key]: value} );
  },
  - getItem(key) {
  - return _localStorage[key] || null;
  + getItem(key: string): string | null {
  + return _localStorage.hasOwnProperty(key) ? _localStorage[key] : null;
  },
  clear() {
  _localStorage = {};
  