Test an empty topic.
.. perl::
my $DOM = 'Text::Restructured::DOM';
my $dom = $DOM->new('topic');
$dom;
.. perl::
my $DOM = 'Text::Restructured::DOM';
my $dom = $DOM->new('topic');
$dom->append($DOM->new('title')
->append($DOM->newPCDATA('Title but no content')));
$dom;