code: public function remove($key)
      {
          $this->open();
          if (isset($_SESSION[$key])) {
              $value = $_SESSION[$key];
              unset($_SESSION[$key]);
  
              return $value;
          } else {
              return null;
          }
      }
docs: Removes a session variable.
  @param string $key the name of the session variable to be removed
  @return mixed the removed value, null if no such session variable.