Why @MockBean does not mock my target repository class (returns null)? [duplicate]

Here is the class I want to test

@Component
public class PermissionCheck {

    @Autowired
    private MyEntityRepository myEntityRepository;

    public boolean hasPermission(int myEntityID) {
        MyEntity myEntity = myEntityRepository.findById(myEntityId);
        return myEntity != null;
    }
}

Here is the test class

@RunWith(SpringRunner.class)
public class PermissionCheckTests {

    @MockBean
    private MyEntityRepository myEntityRepository;

    private PermissionCheck permissionCheck;

    @Before
    public void before() {
        this.permissionCheck = new PermissionCheck();
    }

    @Test
    public void shouldHasPermission() {
        MyEntity myEntity = new MyEntity();

        when(this.myEntityRepository.findById(any())).thenReturn(myEntity);
        assertTrue(this.permissionCheck.hasPermission(0));
    }
}

And when I run this test I got

java.lang.NullPointerException
    at PermissionCheck.hasPermission(PermissionCheck.java:line1)
    at PermissionCheckTests.shouldHasPermission(PermissionCheckTests.java:line2)

In the above, line1 and line2 refer to these two lines

        MyEntity myEntity = myEntityRepository.findById(myEntityId);

        assertTrue(this.permissionCheck.hasPermission(0));

And using debugger I see that when entering PermissionCheck.hasPermission from PermissionCheckTests.shouldHasPermission, the repository field

    @Autowired
    private MyEntityRepository myEntityRepository;

is null.

I created these classes by referring to others existing codes, from different places, and without really understanding how to the annotations (partially due to running out of time), so if someone can tell me not only how to fix, but also why I'm wrong, I would really appreciate it!