The border line cannot be displayed properly after merging cells

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`$writer = new XLSXWriter();
$colOptions = [
'font'=>'Arial',
'font-size'=>15,
'font-style'=>'bold',
'halign'=>'center',
'valign'=>'center',
];
$colOptions_1 = [
'font'=>'Arial',
'font-size'=>13,
'font-style'=>'bold',
'halign'=>'center',
'valign'=>'center',
'border'=>'left,right,top,bottom',
'border-style'=>'thin',
'fill'=>'#d9e1f2',
'string_format'=>'@'
];

    $writer->writeSheetHeader('Sheet1', ['xxx'=>'string'],$colOptions);
    $writer->markMergedCell('Sheet1', 0,0,0,9);
    $writer->writeSheetRow('Sheet1',['xxx'],$colOptions_1);
    $writer->markMergedCell('Sheet1', 1,0,1,9);

`