问如何模拟RestTemplate交换？

EN

java.lang.NullPointerException: Cannot invoke "com.fasterxml.jackson.databind.JsonNode.asText()" because the return value of "com.fasterxml.jackson.databind.JsonNode.get(String)" is null

public class AssignmentService implements AssignemetServiceInterface {
    @Autowired
    AppInterceptor appInterceptor;
    @Autowired
    AssignmentRepository assignmentRepository;
    @Autowired
    private RestTemplate restTemplate;
    private String uri="http://localhost:8080/api/users/"+uuid;

    @Override
    public List<String> assignApplicationsToUser(List<String> applications, String uuid)
            throws SQLException, RequestEntityNotFoundException {

        HttpHeaders headers = new HttpHeaders();
        headers.set("token", appInterceptor.getLoggedInUser());
        HttpEntity<String> requestEntity = new HttpEntity<>(null, headers);
        String result = restTemplate.exchange(uri, HttpMethod.GET, requestEntity, String.class).getBody();

        ObjectMapper objectMapper = new ObjectMapper();
        List<String> response = new ArrayList<>();
        JsonNode responseJson = objectMapper.readTree(result);
        if (responseJson.get("data") == null
                    && responseJson.get("error").get("status").asText().equals("NOT_FOUND")) {
                throw new RequestEntityNotFoundException(uuid, "find");
        }

        for (String application : applications) {
        ApplicationAssignment isAssigned = assignmentRepository.findOneByApplicationId(application);
            if (isAssigned != null) {
                isAssigned.setIsUser(true);
                response.add(application + " reassigned to "+ uuid);
                isAssigned.setAssignedTo(uuid);
                this.assignmentRepository.save(isAssigned);
                } 
           else {
          ApplicationAssignment newApplication = new ApplicationAssignment(application, uuid, true);
    
            this.assignmentRepository.save(newApplication);
            response.add(application + " assigned successfully");
        }
       }
    return response;
}
}

{
    "data": {
        "id": "fa727274-5a74-428a-b0f6-501eebafd8e8",
        "name": "Akash",
        "email": "AkashTyagi@fico.com",
        "phone": 8799190991,
        "isActive": true,
        "createdBy": "abhishekjaiswal@fico.com",
        "updatedBy": null,
        "creationTimeStamp": "2021-08-11T11:23:05.356+00:00",
        "updationTimeStamp": null
    },
    "error": null,
    "timeStamp": "2021-08-16T05:02:04.866+00:00",
    "success": true
}

@RunWith(MockitoJUnitRunner.class)
@SpringBootTest
public class AssignmentServiceTest {

    private static final Logger LOGGER = LoggerFactory.getLogger(AssignmentServiceTest.class);
    @InjectMocks
    private AssignmentService assignmentService;
    
    @Mock
    private AssignmentRepository assignmentRepo;
    
    @Mock
    private AppInterceptor appInterceptor;
    
    @Mock
    private RestTemplate restTemplate;
    
    ObjectMapper  objectMapper;
    String jsonString="{\r\n"
            + "    \"data\": {\r\n"
            + "        \"id\": \"fa727274-5a74-428a-b0f6-501eebafd8e8\",\r\n"
            + "        \"name\": \"Akash\",\r\n"
            + "        \"email\": \"AkashTyagi@fico.com\",\r\n"
            + "        \"phone\": 8799190991,\r\n"
            + "        \"isActive\": true,\r\n"
            + "        \"createdBy\": \"abhishekjaiswal@fico.com\",\r\n"
            + "        \"updatedBy\": null,\r\n"
            + "        \"creationTimeStamp\": \"2021-08-11T11:23:05.356+00:00\",\r\n"
            + "        \"updationTimeStamp\": null\r\n"
            + "    },\r\n"
            + "    \"error\": null,\r\n"
            + "    \"timeStamp\": \"2021-08-16T05:02:04.866+00:00\",\r\n"
            + "    \"success\": true\r\n"
            + "}";;
            
    JsonNode mock;
    
    @BeforeEach
    private void setUp() throws JsonMappingException, JsonProcessingException {
    
         objectMapper = new ObjectMapper();
         mock = org.mockito.Mockito.mock(JsonNode.class);
    }
    @Test
    public void test_assignApplicationsToUser() throws NullPointerException, SQLException, RequestEntityNotFoundException, IndexOutOfBoundsException,JsonProcessingException, URISyntaxException{

        LOGGER.info("Begin of test_assignApplicationToUser method");

        
        ApplicationAssignment applicationAssignment = new ApplicationAssignment("1","u1",true);
        ApplicationAssignment savedApplicationAssignment = new ApplicationAssignment("1","u2",true);
    

        ResponseEntity<String> myEntity = new ResponseEntity<String>("{\r\"error\":null\r}",HttpStatus.ACCEPTED);
        
        
        Mockito.when(restTemplate.exchange(
                ArgumentMatchers.anyString(),
                ArgumentMatchers.any(HttpMethod.class),
                ArgumentMatchers.any(),
                ArgumentMatchers.<Class<String>>any())).thenReturn(myEntity);
        
        Mockito.when(appInterceptor.getLoggedInUser()).thenReturn("abhishek@fico.com");

     
        Mockito.when(mock.get("data")).thenReturn(mock);
        Mockito.when(mock.get("error")).thenReturn(mock);
        Mockito.when(mock.get("error").asText()).thenReturn("FOUND");
        LOGGER.info("Node value "+ mock.asText());
        
        Mockito.when(assignmentRepo.findOneByApplicationId("1")).thenReturn(applicationAssignment);
        Mockito.when(assignmentRepo.save(ArgumentMatchers.any())).thenReturn(savedApplicationAssignment);
 
        // Mock the input List of applications
        List<String> listOfApplication = new ArrayList<>();
        listOfApplication.add("app1");
        listOfApplication.add("app2");
        List<String> response = assignmentService.assignApplicationsToUser(listOfApplication,"u1");
        assertEquals(response.get(0),"app1 assigned successfully");
    }
}