我需要通过调用一个外部api来进行测试，在这里我执行以下操作：
服务等级：

public class BatchStatusClient {

    @Value("${batchStatusUpdate.username}")
    private String username;

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

    public BatchStatusClient(@Value("${batchStatusUpdate.endpoint}")
            String urlBatchStatusUpdate) {
        this.webClient = WebClient.create("urlBatchStatusUpdate");
    }

    public Mono<JsonNode> getToken(String uuid) {
        return this.webClient.post()
                .uri("/authorization")
                .headers(httpHeaders1 -> {
                    httpHeaders1.setBasicAuth(username, password);
                    httpHeaders1.add(REQUEST_ALLOW_ORIGIN, "*");
                    httpHeaders1.add(REQUEST_ALLOW_CREDENTIALS, "false");
                    httpHeaders1.add(HttpHeaders.CONTENT_TYPE,
                            MediaType.APPLICATION_FORM_URLENCODED_VALUE);
                })
                .body(BodyInserters.fromFormData("grant_type", grantType))
                .retrieve()
                .bodyToMono(JsonNode.class);
    }
}

测试等级：

@TestPropertySource(locations = "classpath:/application-dev.yml")
@SpringBootTest()
@ExtendWith(SpringExtension.class)
@ActiveProfiles("dev")
@ContextConfiguration(classes = BatchStatusClient.class)
public class BatchStatusClientTest {

    private BatchStatusClient batchStatusClient;

    private static MockWebServer mockWebServer;

    @BeforeEach
    public void setup() throws IOException {
        mockWebServer = new MockWebServer();
        mockWebServer.start(9090);
        this.batchStatusClient = new BatchStatusClient(
                mockWebServer.url("/").toString());
    }

    @AfterAll
    static void tearDown() throws IOException {
        mockWebServer.shutdown();
    }

    @Test
    public void test_getToken() throws Exception {
        String jsonString = "{\"access_token\": \"QB7VGhGtQWEXB3J98lIjF3\"}";
        ObjectMapper mapper = new ObjectMapper();
        JsonNode jn = mapper.readTree(jsonString);

        mockWebServer.enqueue(new MockResponse()
                .setBody(new ObjectMapper().writeValueAsString(jn))
                .addHeader(HttpHeaders.CONTENT_TYPE,
                        MediaType.APPLICATION_JSON_VALUE));
        Mono<JsonNode> result = batchStatusClient.getToken("123");
        System.out.println("result = " + result);
        assertEquals("QB7VGhGtQWEXB3J98lIjF",
                result.block().get("access_token").asText());
    }
}

但当我运行测试时，出现以下异常：

java.lang.IllegalArgumentException: Username must not be null
  at org.springframework.util.Assert.notNull(Assert.java:201)
  at org.springframework.http.HttpHeaders.encodeBasicAuth(HttpHeaders.java:1834)
  at org.springframework.http.HttpHeaders.setBasicAuth(HttpHeaders.java:770)
  at org.springframework.http.HttpHeaders.setBasicAuth(HttpHeaders.java:751)

我应该做额外的配置吗？