The following is wrong since ' ' is true:

    my $dbh = shift ||' ';
    my $sth = shift ||' ';

    ...

    $sth->finish()     if $sth;
    $dbh->disconnect() if $dbh;
[download]

The above is equivalent to:

    my $dbh = shift;
    my $sth = shift;

    ...

    if ($sth) {
       $sth->finish();
    } else {
       ' '->finish();  # RUNTIME ERROR
    }

    if ($sth) {
       $dbh->disconnect();
    } else {
       ' '->diconnect();  # RUNTIME ERROR
    }
[download]

Why not just do this:

    my $dbh = shift;
    my $sth = shift;

    ...

    $sth->finish()     if $sth;
    $dbh->disconnect() if $dbh;
[download]