$div->set_child_content(class => 'solution', literal $data->{solution});
$div->fclass('problem')->namedlink($data->{id}, $data->{name});
};
- my @pb = map { @{$args{$_}} } qw/beginner easy medium hard/;
+ my @pb = map { @{$args{$_} // []} } qw/beginner easy medium hard/;
$tree->fclass('well')->iter3(\@pb, $iter);
}