if (Party.readByContributorNumber(socialSecurityNumber) != null) {
final Party existingContributor = Party.readByContributorNumber(socialSecurityNumber); if (existingContributor != null && existingContributor != this) {
    public void setSocialSecurityNumber(String socialSecurityNumber) {        if (Party.readByContributorNumber(socialSecurityNumber) != null) {            throw new DomainException("PERSON.createContributor.existing.contributor.number");        }        super.setSocialSecurityNumber(socialSecurityNumber);    }