Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
public function writeBlank($row, $col, $xfIndex)
    {
        $record = 0x0201; // Record identifier
        $length = 0x0006; // Number of bytes to follow

        $header = pack('vv', $record, $length);
        $data = pack('vvv', $row, $col, $xfIndex);
        $this->append($header . $data);

        return 0;
    }
public function writeBlank($row, $col, $xfIndex)
    {
        $record = 0x0201; // Record identifier
        $length = 0x0006; // Number of bytes to follow

        $header = pack('vv', $record, $length);
        $data = pack('vvv', $row, $col, $xfIndex);
        $this->append($header . $data);

        return 0;
    }
Write a blank cell to the specified row and column (zero indexed).
A blank cell is used to specify formatting without adding a string
or a number.

A blank cell without a format serves no purpose. Therefore, we don't write
a BLANK record unless a format is specified.

Returns  0 : normal termination (including no format)
-1 : insufficient number of arguments
-2 : row or column out of range

@param int $row Zero indexed row
@param int $col Zero indexed column
@param mixed $xfIndex The XF format index

@return int