person.changeUsername(null, persons);
person.changeUsername(null);
	public void testChangeUsername() {		Person person = new Person(infoPerson1, country);		person.setUsername("user1");		Person person2 = new Person(infoPerson2, country);		person2.setUsername("user2");		Person person3 = new Person(infoPerson3, country);		person3.setUsername("user3");		List<Person> persons = new ArrayList<Person>();		persons.add(person);		persons.add(person2);		persons.add(person3);		person.changeUsername("newUsername", persons);		assertEquals(person.getUsername(), "newUsername");		try {			person.changeUsername("user2", persons);			fail("Username already exists - should have thrown a DomainException");		} catch (DomainException domainException) {			// caught expected exception		}		assertEquals(person.getUsername(), "newUsername");		try {			person.changeUsername("", persons);			fail("Empty username - should have thrown a DomainException");		} catch (DomainException domainException) {			// caught expected exception		}		assertEquals(person.getUsername(), "newUsername");		try {			person.changeUsername(null, persons);			fail("Null username - should have thrown a DomainException");		} catch (DomainException domainException) {			// caught expected exception		}		assertEquals(person.getUsername(), "newUsername");	}