@Override public void addUnitToPerson(ProposalPerson person, ProposalPersonUnit unit) { if (unit == null) { throw new IllegalArgumentException("Cannot add null units to a ProposalPerson instance"); } if (!person.containsUnit(unit.getUnitNumber())) { unit.setProposalPerson(person); person.addUnit(unit); unit.refreshReferenceObject("unit"); } }