/**
  * Constructor.
  *
  * @param array  $date_query
  * @param string $column
  *
  * @see WP_Date_Query::__construct()
  */
 public function __construct($date_query, $column = '')
 {
     if (!empty($column)) {
         $this->column = $column;
         add_filter('date_query_valid_columns', array($this, 'register_date_column'));
     }
     parent::__construct($date_query, $column);
 }