Test metody dodawania elementu do bazy danych nie działa

 	public Optional<PersonDto> addPerson(PersonDto personDto) {
		Assert.notNull(personDto, "personDto can't be null");
		Person person = personRepository
				.save(modelMapper.map(personDto, Person.class));
		return Optional.of(modelMapper.map(person, PersonDto.class));
	}

	@Test
	public void shouldAddPersonToDatabase() {
		Person person1 = new Person(1L, "jan", "mucha", "krakow", "email1@onet.com", "Programing", "Developer");
		personService.addPerson(mapper.map(person1, PersonDto.class));
		Mockito.verify(personRepository, times(1)).save(person1);
	}

java.lang.IllegalArgumentException: source cannot be null

	at org.modelmapper.internal.util.Assert.notNull(Assert.java:53)
	at org.modelmapper.ModelMapper.map(ModelMapper.java:370)
	at com.softwaremind.crew.people.service.PersonService.addPerson(PersonService.java:85)
	at com.softwaremind.crew.people.service.PersonServiceTest.shouldAddPersonToDatabase(PersonServiceTest.java:75)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

	private PersonService personService;
	private ModelMapper mapper;
	
	@Mock
	private PersonRepository personRepository;
	
	@Before
	public void initTest() {
		MockitoAnnotations.initMocks(this);
		mapper = new ModelMapper();
		personService = new PersonService(personRepository, this.mapper);

	}

	@Before
	public void initMockRepository() {
		Person person1 = new Person(1L, "jan", "mucha", "krakow", "email1@ont.com", "Programing", "Developer");
		Person person2 = new Person(1L, "Alicja", "Kowalska", "Warszawa", "email2@gmail.com", "Business", "Designer");
		Mockito.when(personRepository.findAll()).thenReturn(Arrays.asList(person1, person2));
	}

public void addPerson(PersonDto personDto) {
		Assert.notNull(personDto);
		Assert.notNull(personDto.getFirstName());
		personRepository.save(modelMapper.map(personDto, Person.class));
	}