Just replace (near line 166)

$tot_HT = ($tot_sale['total']-$tot_shipping['total'])*(1-($tot_taxes['total']/$tot_sale['total']));

by

if($tot_sale['total'] == 0){
$tot_HT = 0;
$tot_sale['total'] = 0;
}else{
$tot_HT = ($tot_sale['total']-$tot_shipping['total'])*(1-($tot_taxes['total']/$tot_sale['total']));
}
I think now it works

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