-sub get_duedate {
-  $main::lxdebug->enter_sub();
-
-  my ($self, $myconfig, $reference_date) = @_;
-
-  my $terms   = $self->{payment_id}  ? SL::DB::PaymentTerm->new(id => $self->{payment_id}) ->load
-              : $self->{customer_id} ? SL::DB::Customer   ->new(id => $self->{customer_id})->load->payment
-              : $self->{vendor_id}   ? SL::DB::Vendor     ->new(id => $self->{vendor_id})  ->load->payment
-              : $self->{invdate}     ? undef # no payment terms, therefore invdate == duedate
-              :                        croak("Missing field in \$::form: payment_id, customer_id, vendor_id or invdate");
-  my $duedate = $terms ? $terms->calc_date(reference_date => $reference_date)->to_kivitendo : undef;
-
-  $main::lxdebug->leave_sub();
-
-  return $duedate;
-}
-