[Perl]Return values of nullable are not correct.

Test Build:CUBRID 2008 R4.0 (8.4.0.2019) (64bit release build for linux_gnu)
OS: Linux 64
Description: Return values of nullable are not correct.

Repro Steps:
perl nullable_02.pl

statements in nullable_02.pl:
$dbh -> do("create table coo(id int not null primary key auto_increment,col4 bit(8), phone int );")
$dbh->do("insert into coo values(NULL,b'0011', 1234);") or die "insert error: $dbh->errstr";

my $sth=$dbh->prepare("select * from coo") or die "prepare error: $dbh->errstr";
$sth->execute() or die "execute error: $dbh->errstr";
my $fieldNumber=$sth->{NUM_OF_FIELDS};
print "Number of field is $fieldNumber\n";

for (my $i=0;$i<$fieldNumber; $i++){
print "name: $sth->{NAME}->[$i]\n";
print "nullable: $sth->{NULLABLE}->[$i]\n\n\n";
}

Actual result:

Number of field is 3
name: id
nullable: 0


name: col4
nullable: 8


name: phone
nullable: 0

Expect result:

Number of field is 3
name: id
nullable: 


name: col4
nullable: 1


name: phone
nullable: 1