message: Fix: prevent the PopDownNumber dialog from crashing
diff: @@ -48,7 +48,8 @@ export class PopDownNumberDialog extends TemplatedElementBase {
  }
  protected _themeCssFiles(): ThemeTypes.CssFile[] {
  - return [ThemeTypes.CssFile.GENERAL_GUI, ThemeTypes.CssFile.FONT_AWESOME, ...this._extraCssFiles];
  + const extraCssFiles = this._extraCssFiles == null ? [] : this._extraCssFiles;
  + return [ThemeTypes.CssFile.GENERAL_GUI, ThemeTypes.CssFile.FONT_AWESOME, ...extraCssFiles];
  }
  getValue(): number {
  