testing if a JSON property is null in a Spring Boot integration test

Question

In a Spring Boot integration test, I'm trying to test if a JSON property is null

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class IntegrationTests {

    @Autowired
    private WebTestClient webClient;

    @Test
    void saveExtension() {
        webClient.get()
            .uri("/api/endpoint")
            .exchange()
            .expectStatus()
            .is2xxSuccessful();
            .expectBody()
            .jsonPath("$.data[0].extended").isEqualTo(null)
    }
}

The test passes, but I get a SpotBugs error (and an IntelliJ warning) because the parameter of isEqualTo is annotated @NotNull.

Surely there's a more elegant way of testing whether a JSON property is null? I've tried both of the following alternatives provided by org.springframework.test.web.reactive.server.JsonPathAssertions:

• .jsonPath("$.data[0].extended").doesNotExist()
• .jsonPath("$.data[0].extended").isEmpty()

But the test fails in both cases. Is there a better way of testing if a JSON property is null?

I also tried the following:

import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.nullValue;
// ...
.jsonPath("$.data[?(@.bidderId == '%s')].extended", BIDDER_ID_2).value(is(nullValue()));

But this fails with the error:

Expected: is null but: was <[null]>

This error message suggests that extended: [null] was returned but I've checked the response and it's extended: null