public function addRow(array $row)
    {
        if (is_array($this->fields)) {
            $assoc = $row;
            $row = [];
            foreach ($this->fields as $field) {
                $row[] = isset($assoc[$field]) ? $assoc[$field] : "";
            }
        }

        $this->data[] = $row;

        return $this;
    }