#vulnerable code 
                              @Test
  public void testDeleteInstanceIdError() throws Exception {
    final MockLowLevelHttpResponse response = new MockLowLevelHttpResponse();
    MockHttpTransport transport = new MockHttpTransport.Builder()
        .setLowLevelHttpResponse(response)
        .build();
    FirebaseOptions options = FirebaseOptions.builder()
        .setCredentials(new MockGoogleCredentials("test-token"))
        .setProjectId("test-project")
        .setHttpTransport(transport)
        .build();
    FirebaseApp app = FirebaseApp.initializeApp(options);

    // Disable retries by passing a regular HttpRequestFactory.
    FirebaseInstanceId instanceId = new FirebaseInstanceId(app, transport.createRequestFactory());
    TestResponseInterceptor interceptor = new TestResponseInterceptor();
    instanceId.setInterceptor(interceptor);

    try {
      for (int statusCode : ERROR_CODES.keySet()) {
        response.setStatusCode(statusCode).setContent("test error");

        try {
          instanceId.deleteInstanceIdAsync("test-iid").get();
          fail("No error thrown for HTTP error");
        } catch (ExecutionException e) {
          assertTrue(e.getCause() instanceof FirebaseInstanceIdException);
          checkFirebaseInstanceIdException((FirebaseInstanceIdException) e.getCause(), statusCode);
        }

        assertNotNull(interceptor.getResponse());
        HttpRequest request = interceptor.getResponse().getRequest();
        assertEquals(HttpMethods.DELETE, request.getRequestMethod());
        assertEquals(TEST_URL, request.getUrl().toString());
      }
    } finally {
      app.delete();
    }
  } 
                            #location 32 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              @Test
  public void testDeleteInstanceIdError() throws Exception {
    final MockLowLevelHttpResponse response = new MockLowLevelHttpResponse();
    MockHttpTransport transport = new MockHttpTransport.Builder()
        .setLowLevelHttpResponse(response)
        .build();
    FirebaseOptions options = APP_OPTIONS.toBuilder()
        .setHttpTransport(transport)
        .build();
    FirebaseApp app = FirebaseApp.initializeApp(options);

    // Disable retries by passing a regular HttpRequestFactory.
    FirebaseInstanceId instanceId = new FirebaseInstanceId(app, transport.createRequestFactory());
    TestResponseInterceptor interceptor = new TestResponseInterceptor();
    instanceId.setInterceptor(interceptor);

    try {
      for (int statusCode : ERROR_CODES.keySet()) {
        response.setStatusCode(statusCode).setContent("test error");

        try {
          instanceId.deleteInstanceIdAsync("test-iid").get();
          fail("No error thrown for HTTP error");
        } catch (ExecutionException e) {
          assertTrue(e.getCause() instanceof FirebaseInstanceIdException);
          checkFirebaseInstanceIdException((FirebaseInstanceIdException) e.getCause(), statusCode);
        }

        assertNotNull(interceptor.getResponse());
        HttpRequest request = interceptor.getResponse().getRequest();
        assertEquals(HttpMethods.DELETE, request.getRequestMethod());
        assertEquals(TEST_URL, request.getUrl().toString());
      }
    } finally {
      app.delete();
    }
  }