protected function normalize($default)
    {
        if ($this->is('empty')) {
            return;
        }

        $maxCols = array_reduce(
                $this->data,
                function($carry, $item) {
                    $l = count($item);
                    return ($l > $carry ? $l : $carry);
                },
                0);

        array_walk(
                $this->data,
                function(&$row) use ($maxCols, $default) {
                    if (($len = count($row)) < $maxCols) {
                        $row += array_fill($len, $maxCols - $len, $default);
                    }
                });
    }