MySQL oddities

output

1: got user $VAR1 = {
          'uid' => '1'
        };
 with undef uid!

2: ok (didn't find a user)

test.pl

#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;
$Data::Dumper::Sortkeys = 1;

use DBI;
my %conf = (
	dsn => 'dbi:mysql:database=my_test;host=localhost',
	dbuser => 'me',
	dbpass => undef,
);
my $dbh = DBI->connect($conf{'dsn'}, $conf{'dbuser'}, $conf{'dbpass'}, {RaiseError => 1, AutoCommit => 1});

$dbh->do('DROP TABLE IF EXISTS test_users');
$dbh->do('CREATE TABLE test_users (uid INTEGER PRIMARY KEY AUTO_INCREMENT, name varchar(20) NOT NULL);');

{
	my $sth = $dbh->prepare('INSERT INTO test_users(name) values(?)');
	$sth->execute('asdf' . time);
}

# If I uncomment this line, the problem disappears
#$dbh = DBI->connect($conf{'dsn'}, $conf{'dbuser'}, $conf{'dbpass'}, {RaiseError => 1, AutoCommit => 1});

for (1 .. 2) {
	my $user;
	# Load the user
	my $sth = $dbh->prepare('SELECT uid FROM test_users WHERE uid IS NULL');
	$sth->execute;
	while (my $row = $sth->fetchrow_hashref()) {
		$user = Dumper($row);
	}
	if ($user) {
		print "$_: got user $user with undef uid!\n\n";
	} else {
		print "$_: ok (didn't find a user)\n";
	}
}