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);

`