private function fillCells($row)
    {
        $newRow = [];
        foreach ($row as $column => $cell) {
            $newRow[] = $cell;
            if ($cell instanceof TableCell && $cell->getColspan() > 1) {
                foreach (range($column + 1, $column + $cell->getColspan() - 1) as $position) {
                    // insert empty value at column position
                    $newRow[] = '';
                }
            }
        }

        return $newRow ?: $row;
    }