message: Fix a small null pointer
diff: @@ -180,6 +180,9 @@ export class PopDownListPicker<T extends { id: string; }> extends ThemeableEleme
  private _scrollToSelected(): void {
  const resultsDiv = DomUtils.getShadowId(this, ID_RESULTS);
  const selectedElement = <HTMLElement> resultsDiv.querySelector("." + PopDownListPicker.CLASS_RESULT_SELECTED);
  + if (selectedElement == null) {
  + return;
  + }
  const selectedRelativeTop = selectedElement.offsetTop - resultsDiv.offsetTop;
  resultsDiv.scrollTop = selectedRelativeTop;
  }
  