public function allNumberFormats(Spreadsheet $spreadsheet)
    {
        // Get an array of unique number formats
        $aNumFmts = [];
        $aStyles = $this->allStyles($spreadsheet);

        /** @var \PhpOffice\PhpSpreadsheet\Style\Style $style */
        foreach ($aStyles as $style) {
            if ($style->getNumberFormat()->getBuiltInFormatCode() === false && !isset($aNumFmts[$style->getNumberFormat()->getHashCode()])) {
                $aNumFmts[$style->getNumberFormat()->getHashCode()] = $style->getNumberFormat();
            }
        }

        return $aNumFmts;
    }