Why does $product->brand_supplier return null?


## Query and result
select p.product_id, bs.brand_supplier_id, b.brand_id, b.name
from product as p
left join brand_supplier as bs
    on bs.brand_supplier_id=p.brand_supplier_id
left join brand as b
    on b.brand_id=bs.brand_id
where p.product_id=7797923;
+------------+-------------------+----------+--------+
| product_id | brand_supplier_id | brand_id | name   |
+------------+-------------------+----------+--------+
|    7797923 |               492 |        1 | adidas |
+------------+-------------------+----------+--------+

## Product.pm
package Mine::DBIx::Schema::Result::Product;
use base qw/DBIx::Class::Core/;

__PACKAGE__->table('product');
__PACKAGE__->add_columns(qw/ name product_id description fraud_percent /);
__PACKAGE__->set_primary_key('product_id');
__PACKAGE__->has_one(brand_supplier => 'Mine::DBIx::Schema::Result::BrandSupplier', brand_supplier_id);
__PACKAGE__->has_many(styles => 'Mine::DBIx::Schema::Result::Style', product_id);
1;


## Brand.pm
package Mine::DBIx::Schema::Result::Brand;
use base qw/DBIx::Class::Core/;
__PACKAGE__->table('brand');
__PACKAGE__->add_columns(qw/ name is_kids is_couture is_handbag brand_id /);
__PACKAGE__->set_primary_key('brand_id');
__PACKAGE__->belongs_to(brand_supplier => 'Mine::DBIx::Schema::Result::BrandSupplier', 'brand_id');
1;

## BrandSupplier.pm
package Mine::DBIx::Schema::Result::BrandSupplier;
use base qw/DBIx::Class::Core/;

__PACKAGE__->table('brand_supplier');
__PACKAGE__->add_columns(qw/ brand_id brand_supplier_id/);
__PACKAGE__->set_primary_key('brand_supplier_id');
__PACKAGE__->has_one(brand => 'Mine::DBIx::Schema::Result::Brand', 'brand_id');
__PACKAGE__->belongs_to(product => 'Mine::DBIx::Schema::Result::Product', 'brand_supplier_id');

1;

### Script:
#!/usr/bin/perl -w

use strict;
use Mine::DBIx::Schema;
use Data::Dumper;

my $dsn = 'DBI:mysql:database=product;host=localhost';
my $user = 'user';
my $pass = 'pass';
my $schema = Mine::DBIx::Schema->connect($dsn, $user, $pass);

my $product = get_product( 7797923 );

print "Product name: " . $product->name . " and product id is " . $product->product_id ."\n";
print Dumper($product->brand_supplier);

sub get_product {
    my $product_id = shift;
    return $schema->resultset('Product')->search( { product_id => $product_id } )->single;
}

## This returns this output:
Use of uninitialized value in scalar assignment at /usr/lib64/perl5/site_perl/5.8.8/x86_64-linux-thread-multi/List/MoreUtils.pm line 24.
Product name: Barracks Premier Wide and product id is 7797923
$VAR1 = undef;