模拟测试中的NullPointerException

Question

我是初学者，我需要你的帮助！

我有这堂课：

public class MyClass {
    private IService1 service1;
    private IService2 service2;

    public void setService1(final IService1 service1) {
        this.service1 = service1;
    }

    public MyList myMethod(final Param param) throws MyException {
        final MyList list = method2(param);
        if (list.isEmpty()) {      //here it throws a null pointer exception, because the mock didn't return "list" from my test
            throw new MyException("Blablabla");
        }
        return list;
    }

param有一个Collection myObjList，有两个list，list1和list2。

以下是method2的作用：

private MyList method2(final Param param) {
    Collection<MyObj> myObjList = CollectionUtils.isEmpty(param.getMyObjList) ? list1 : list2;
    MyList list = new MyList(new HashSet<>(myObjList), false);
    return service1.filter(list, param);    
}

我做了一个测试并模拟了service1，但是我有一个nullPointerException，我不明白为什么。

以下是测试：

@RunWith(MockitoJUnitRunner.class)
public class MyClassTest {
    @InjectMocks
    private  MyClass myClass;

    @Mock
    private IService1 service1;

    @Test
    public void test() throws MyException {
        //Given
        Param param = create_param(); //this is OK
        MyList list = new MyList();
        list.add("something");
        when(service1.filter(any(), any())).thenReturn(list); //doesn't return list

        //When
        MyList myObjList = myClass.method(param);

        //Then
        assertThat(myObjList).isNotNull();
        assertThat(myObjList.size()).isEqualTo(1);
    }

你能帮我理解我的错误吗？

提前致谢