Upgrade from Spring 5.2.15 to 5.3.0 - mock is null

My project uses JDK 8, and I have a test class

...
    import org.mockito.Mock;
    import org.mockito.stubbing.Answer;
    
    import javax.servlet.FilterChain;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
...

 @ExtendWith(MockitoExtension.class)
 class ForwardedHeaderFilterTest {

    private MyForwardedHeaderFilter forwardedHeaderFilter;

    @Mock
    private HttpServletRequest httpServletRequest;

    @Mock
    private HttpServletResponse httpServletResponse;
....

with a test

@Test
void doFilterInternal_forwardedHeader_withPort() throws ServletException, IOException {
    // Given
    String ip = "12.34.56.78";
    int clientPort = 1234;
    mockForwardedHeader(ip, clientPort, "https");

    // When
    forwardedHeaderFilter.doFilterInternal(httpServletRequest, httpServletResponse, filterChain);
....

It all works fine in Spring 5.2.x, after upgrading (or rather trying to) to 5.3.x, the mocked variable httpServletResponse becomes null. Has anyone experienced the same issue?

Is there a relation to this issue, perhaps?