/**
  * Returns the instance.
  *
  * @since  1.2.0
  * @return object
  */
 public static function get_instance($handler_file = null)
 {
     // If the single instance hasn't been set, set it now.
     if (null == self::$instance) {
         self::$instance = new self($handler_file);
     }
     return self::$instance;
 }