for my $attr (qw( country customer_number ticket_type )) {
    my $reader  = "get_$attr";
    my $clearer = "clear_$attr";
    has $attr => (
            is        => 'rw',
            reader    => $reader,
            writer    => "set_$attr",
            predicate => "has_$attr",
            clearer   => $clearer,
            trigger   => sub {
                my ($self)  = @_;
                if (! defined $self->$reader || $self->$reader eq '' )
+ {
                    $self->$clearer;
                }
            }
    );
}
[download]

Notice I switched the two conditions in the || to prevent warnings about undefined.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]