Please pay attention to the following points:

1. Are you using @org.mockito.InjectMocks?

2. JUnit version:

   2.1) If it’s JUnit 4, configure the test class as follows:

   @org.junit.Before
   public void setUp() {
       org.mockito.MockitoAnnotations.openMocks(this);
   }
   

   2.2) If it’s JUnit 5:

   @org.junit.BeforeEach
   void setUp() {
       MockitoAnnotations.openMocks(this);
   }
   

3. In my case, I am not using @ExtendWith(MockitoExtension.class) in the class.