my $comment;
$comment = $wsheet->Cells($row_num,$col_num)->{Comment};
if(defined $comment)
{
    $wsheet->Cells($row_num,$col_num)->{Comment}->Text({Text => $cell_value});
}
else
{
    $wsheet->Cells($row_num,$col_num)->AddComment($cell_value);
    $comment = $wsheet->Cells($row_num,$col_num)->{Comment};
    if(!defined $comment) {
        print STDERR "Could not add comment in row $row_num and column $col_num\n";
    }
}