Can't show false values

[TakeAsh]

I tried to show "false values" (0, blank) in span tag, but it failed.

t/builder_xml_falsevalues.t

use strict;
use Test::More;
use Builder;

subtest 'False Values' => sub {
    my @testCases = (
        { input => undef, expected => '<span />',       name => 'undef' },
        { input => 0,     expected => '<span>0</span>', name => '0' },
        { input => '',    expected => '<span></span>',  name => 'blank' },
    );
    my $builder = Builder->new();
    my $xm      = $builder->block('Builder::XML');
    foreach my $testcase (@testCases) {
        $xm->span( $testcase->{input} );
        is( $builder->render, $testcase->{expected}, $testcase->{name} );
    }
};

done_testing;

result

# Subtest: False Values
Use of uninitialized value $args[0] in join or string at /usr/local/share/perl5/Builder/XML.pm line 50.
    ok 1 - undef
    not ok 2 - 0
    #   Failed test '0'
    #   at /home/Shared/builder/t/builder_xml_falsevalues.t line 15.
    #          got: '<span />'
    #     expected: '<span>0</span>'
    not ok 3 - blank
    #   Failed test 'blank'
    #   at /home/Shared/builder/t/builder_xml_falsevalues.t line 15.
    #          got: '<span />'
    #     expected: '<span></span>'
    1..3
    # Looks like you failed 2 tests of 3.
not ok 1 - False Values
#   Failed test 'False Values'
#   at ./t/builder_xml_falsevalues.t line 17.
1..1
# Looks like you failed 1 test of 1.