private function renderRow(RowInterface $row, Collection $columnNames)
    {
        $line = self::CHAR_CELL_SEPARATOR;

        // render cells of the row
        foreach ($columnNames as $columnName) {
            $colWidth = $this->table->getColumnWidth($columnName);
            if ($row->hasCell($columnName)) {
                $cell = $row->getCell($columnName);
                $currentCell = $this->renderCell($cell, $colWidth);
            } else {
                $currentCell = $this->renderCell(new Cell($columnName, ''), $colWidth);
            }

            $line .= $currentCell . self::CHAR_CELL_SEPARATOR;
        }

        return $line;
    }