Issue #3450567 by kalpanajaiswal, joachim: GenerateTheme::__construct() does...

  private $root;

  /**

   * {@inheritdoc}

   * GenerateTheme constructor.

   *

   * @param string|null $name

   *   The name of the command; passing null means it must be set in configure().

   * @param string|null $root

   *   The path for the Drupal root.

   */

  public function __construct(?string $name = NULL, ?string $root = NULL) {

    parent::__construct($name);