Moose Customer Error on Type Constraint Violation

Index.pm

package Index;

use Mouse;
use namespace::autoclean;
use Index::Types;


has 'date'    => (
     is       => 'rw',
     isa      => 'Index::Types::Date',
     coerce   => 1,
     required => 1,
);

__PACKAGE__->meta->make_immutable();

1;

output

$ perl -Ilib test.pl 
Attribute (date) does not pass the type constraint because: This date (2012) is not a valid date! at /opt/perlbrew/perls/cdrtools/lib/site_perl/5.14.2/x86_64-linux/Mouse/Util.pm line 361
	Mouse::Util::throw_error('Mouse::Meta::Attribute=HASH(0x106bce28)', 'Attribute (date) does not pass the type constraint because: T...', 'data', 2012, 'depth', -1) called at test.pl line 6

test.pl

#!/usr/bin/env perl

use Modern::Perl;
use Index;

my $index = Index->new( date => '2012' );

Types.pm

package Index::Types;

use Mouse::Util::TypeConstraints;

subtype 'Index::Types::Date'
        => as 'Str'
        => where { m/\d{8}/ }
        => message { "This date ($_) is not a valid date!"};

coerce 'Index::Types::Date',
    from 'Str',
    via {
          my $digits = $_;
          $digits =~ s/[^\d]//g; # Strip anything that isn't a digit.
          return $digits;
        };
1;