Spring boot Junit Test ResttemplateBuilder build method gives null point Exception

I am trying to cover the circuitBreaker fallback method from the below service class

@Component
public class UserService {
  private static final String UNABLE_TO_CONNECT_TO_USER_SERVICE ="User service not available";
  
  @Value("${user.service.url}")
  private String baseUrl;
  
  @Value("${user.service.username}")
  private String userName;

  @Value("${user.service.password}")
  private String password;

   public UserService(
      RestTemplateBuilder restTemplateBuilder,
      @Qualifier("userService_client_factory")
          HttpComponentsClientHttpRequestFactory httpComponentsClientHttpRequestFactory) {
    var template = restTemplateBuilder.build();
    template.setRequestFactory(httpComponentsClientHttpRequestFactory);
    this.restTemplate = template;
  }

  @CircuitBreaker(name = "userservice", fallbackMethod = "fallback")
  @Loggable
  public User getUser(String userId) {
    try {
      LOGGER.debug("calling getUser for userId {}", userId);
      ResponseEntity<User> responseEntity =
          restTemplate.exchange(
              buildUrl("/v2/{user-id}/user", userId),
              HttpMethod.GET,
              new HttpEntity<>(buildHeaders()),
              new ParameterizedTypeReference<User>() {});

      return responseEntity.getBody();
    } catch (HttpServerErrorException | ResourceAccessException e) {
      throw new ServiceInvokeException(UNABLE_TO_CONNECT_TO_USER_SERVICE, e);
    } catch (RestClientException e) {
      throw new UserException(e.getMessage(), "Get User failed");
    }
  }

  @SuppressWarnings("all")
  private User fallback(String userId, ServiceInvokeException e) {
    throw new ServiceInvokeException(
        format(UNABLE_TO_CONNECT_TO_USER_SERVICE, e.getMessage()), e);
  }

  private HttpHeaders buildHeaders() {
    var headers = new HttpHeaders();
    headers.setAccept(singletonList(APPLICATION_JSON));
    headers.setContentType(APPLICATION_JSON);
    headers.setBasicAuth(userName, password);
    return headers;
  }

  private URI buildUrl(String path, String userId) {
    Map<String, String> pathParameters = new HashMap<>();
    pathParameters.put("user-id", userId);
    String urlPath = baseUrl + path;
    return UriComponentsBuilder.fromUriString(urlPath)
        .buildAndExpand(pathParameters)
        .toUri();
  }
}

below is the Junit Test cases written

@RunWith(SpringRunner.class)
@DirtiesContext
@ContextConfiguration(
  classes = {CircuitBreakerAutoConfiguration.class, UserService.class})
public class UserServiceFallBackTest {

  private static final String USER_NAME = "userName";
  private static final String PASSWORD = "password";
  private static final String USERNAME_VAL = "uname";
  private static final String PWD_VAL = "pwd";
  private static final String userId = "test-userId";
  private static final String ERROR_MESSAGE = "error message";
  @Autowired
  UserService userService;

  @Rule
  public ExpectedException thrown = ExpectedException.none();

  @TestConfiguration
  static class TestConfig {

    @Bean
    RestTemplateBuilder restTemplateBuilder() {
      RestTemplateBuilder restTemplateBuilder = mock(RestTemplateBuilder.class);
      RestTemplate restTemplate = mock(RestTemplate.class);
      ResponseEntity responseEntity = mock(ResponseEntity.class);

      when(restTemplateBuilder.build()).thenReturn(restTemplate);
      when(restTemplate.exchange(
        any(URI.class),
        eq(HttpMethod.GET),
        any(HttpEntity.class),
        any(ParameterizedTypeReference.class)))
        .thenThrow(new HttpServerErrorException(HttpStatus.BAD_GATEWAY));
      return restTemplateBuilder;
    }
    @Bean(name = "userService_client_factory")
    HttpComponentsClientHttpRequestFactory factory(){
      HttpComponentsClientHttpRequestFactory factory = mock(HttpComponentsClientHttpRequestFactory.class);
      return factory;
    }

    @Bean
    UserService userService() {
      return new UserService(restTemplateBuilder(),factory());
    }
  }

  @Test
  public void createFallbackWrapsExceptionAsServiceInvokeException() {
    thrown.expect(ServiceInvokeException.class);
    userService.getUser(userId);
  }

  @Test
  public void createFallbackWrapsExceptionAsRestClientException() {
    thrown.expect(UserException.class);
    userService.getUser(userId);
  }
}

The test case gives NullPointerException at the UserService.java class var template = restTemplateBuilder.build();

here restTemplateBuilder.build() giving null restTemaplate object