Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Spreadsheet.php
public function disconnectWorksheets()
    {
        $worksheet = null;
        foreach ($this->workSheetCollection as $k => &$worksheet) {
            $worksheet->disconnectCells();
            $this->workSheetCollection[$k] = null;
        }
        unset($worksheet);
        $this->workSheetCollection = [];
    }
public function disconnectWorksheets()
    {
        $worksheet = null;
        foreach ($this->workSheetCollection as $k => &$worksheet) {
            $worksheet->disconnectCells();
            $this->workSheetCollection[$k] = null;
        }
        unset($worksheet);
        $this->workSheetCollection = [];
    }
Disconnect all worksheets from this PhpSpreadsheet workbook object,
typically so that the PhpSpreadsheet object can be unset.