message: Fix Unable to find node on an unmounted component
  in
  close ant-design/ant-design#10774
diff: @@ -131,6 +131,11 @@ export default class DropdownMenu extends React.Component {
  }
  return clone(item);
  });
  + } else {
  + // Clear firstActiveItem when dropdown menu items was empty
  + // Avoid `Unable to find node on an unmounted component`
  + // https://github.com/ant-design/ant-design/issues/10774
  + this.firstActiveItem = null;
  }
  // clear activeKey when inputValue change
  