How to get this exception to percolate all the way up to the Plack middleware?

gistfile1.pl

sub reserve_GET : Args(1) {
    my ($self, $c, @args) = @_;

    try {
        my $reserve = Koha::Model::Reserve->new(reservenumber => $args[0])->load;
        $self->status_ok($c, entity=>as_tree($reserve));
    }
    catch {
        if (/^No such Koha::/) {
            HTTP::Exception::404->throw;
        }
        else {
            HTTP::Exception::500->throw;
        }
    };
}