+=item referral_custnum_cust_main
+
+Returns the customer who referred this customer (or the empty string, if
+this customer was not referred).
+
+Note the difference with referral_cust_main method: This method,
+referral_custnum_cust_main returns the single customer (if any) who referred
+this customer, while referral_cust_main returns an array of customers referred
+BY this customer.
+
+=cut
+
+sub referral_custnum_cust_main {
+ my $self = shift;
+ return '' unless $self->referral_custnum;
+ qsearchs('cust_main', { 'custnum' => $self->referral_custnum } );
+}
+