diff --git a/module/spring-boot-restclient-test/build.gradle b/module/spring-boot-restclient-test/build.gradle
index 77e71c54e80..213f653d3fc 100644
--- a/module/spring-boot-restclient-test/build.gradle
+++ b/module/spring-boot-restclient-test/build.gradle
@@ -40,3 +40,7 @@ dependencies {
 
 	testRuntimeOnly("ch.qos.logback:logback-classic")
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}
diff --git a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/MockServerRestClientCustomizerTests.java b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/MockServerRestClientCustomizerTests.java
index 61c8db091fe..1d0a3f86dfc 100644
--- a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/MockServerRestClientCustomizerTests.java
+++ b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/MockServerRestClientCustomizerTests.java
@@ -56,6 +56,7 @@ class MockServerRestClientCustomizerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void createWhenExpectationManagerClassIsNullShouldThrowException() {
 		Class<? extends RequestExpectationManager> expectationManager = null;
 		assertThatIllegalArgumentException().isThrownBy(() -> new MockServerRestClientCustomizer(expectationManager))
@@ -63,6 +64,7 @@ class MockServerRestClientCustomizerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void createWhenExpectationManagerSupplierIsNullShouldThrowException() {
 		Supplier<? extends RequestExpectationManager> expectationManagerSupplier = null;
 		assertThatIllegalArgumentException()
diff --git a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/MockServerRestTemplateCustomizerTests.java b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/MockServerRestTemplateCustomizerTests.java
index 523fe81a4c7..404f92ed7d6 100644
--- a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/MockServerRestTemplateCustomizerTests.java
+++ b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/MockServerRestTemplateCustomizerTests.java
@@ -59,6 +59,7 @@ class MockServerRestTemplateCustomizerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void createWhenExpectationManagerClassIsNullShouldThrowException() {
 		Class<? extends RequestExpectationManager> expectationManager = null;
 		assertThatIllegalArgumentException().isThrownBy(() -> new MockServerRestTemplateCustomizer(expectationManager))
@@ -66,6 +67,7 @@ class MockServerRestTemplateCustomizerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void createWhenExpectationManagerSupplierIsNullShouldThrowException() {
 		Supplier<? extends RequestExpectationManager> expectationManagerSupplier = null;
 		assertThatIllegalArgumentException()
diff --git a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/RootUriRequestExpectationManagerTests.java b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/RootUriRequestExpectationManagerTests.java
index 5539e6ee974..acdb2d9fd44 100644
--- a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/RootUriRequestExpectationManagerTests.java
+++ b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/RootUriRequestExpectationManagerTests.java
@@ -55,6 +55,7 @@ class RootUriRequestExpectationManagerTests {
 	private final String uri = "https://example.com";
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private RequestExpectationManager delegate;
 
 	private RootUriRequestExpectationManager manager;
@@ -65,12 +66,14 @@ class RootUriRequestExpectationManagerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void createWhenRootUriIsNullShouldThrowException() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new RootUriRequestExpectationManager(null, this.delegate))
 			.withMessageContaining("'rootUri' must not be null");
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void createWhenExpectationManagerIsNullShouldThrowException() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new RootUriRequestExpectationManager(this.uri, null))
 			.withMessageContaining("'expectationManager' must not be null");
diff --git a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/AnotherExampleRestClientService.java b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/AnotherExampleRestClientService.java
index 7d1b76821b2..a0c8f98feda 100644
--- a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/AnotherExampleRestClientService.java
+++ b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/AnotherExampleRestClientService.java
@@ -16,6 +16,8 @@
 
 package org.springframework.boot.restclient.test.autoconfigure;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.stereotype.Service;
 import org.springframework.web.client.RestClient;
 import org.springframework.web.client.RestClient.Builder;
@@ -41,7 +43,7 @@ public class AnotherExampleRestClientService {
 		return this.builder;
 	}
 
-	public String test() {
+	public @Nullable String test() {
 		return this.restClient.get().uri("/test").retrieve().toEntity(String.class).getBody();
 	}
 
diff --git a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/AnotherExampleRestTemplateService.java b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/AnotherExampleRestTemplateService.java
index f9a64c94aed..511f1473062 100644
--- a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/AnotherExampleRestTemplateService.java
+++ b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/AnotherExampleRestTemplateService.java
@@ -16,6 +16,8 @@
 
 package org.springframework.boot.restclient.test.autoconfigure;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.restclient.RestTemplateBuilder;
 import org.springframework.stereotype.Service;
 import org.springframework.web.client.RestTemplate;
@@ -38,7 +40,7 @@ public class AnotherExampleRestTemplateService {
 		return this.restTemplate;
 	}
 
-	public String test() {
+	public @Nullable String test() {
 		return this.restTemplate.getForEntity("/test", String.class).getBody();
 	}
 
diff --git a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/ExampleRestClientService.java b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/ExampleRestClientService.java
index 4b19fadbc7f..431e800d311 100644
--- a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/ExampleRestClientService.java
+++ b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/ExampleRestClientService.java
@@ -16,6 +16,8 @@
 
 package org.springframework.boot.restclient.test.autoconfigure;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.stereotype.Service;
 import org.springframework.web.client.RestClient;
 import org.springframework.web.client.RestClient.Builder;
@@ -42,7 +44,7 @@ public class ExampleRestClientService {
 		return this.builder;
 	}
 
-	public String test() {
+	public @Nullable String test() {
 		return this.restClient.get().uri("/test").retrieve().toEntity(String.class).getBody();
 	}
 
diff --git a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/ExampleRestTemplateService.java b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/ExampleRestTemplateService.java
index 4a01d175de9..4f04ecdd472 100644
--- a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/ExampleRestTemplateService.java
+++ b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/ExampleRestTemplateService.java
@@ -16,6 +16,8 @@
 
 package org.springframework.boot.restclient.test.autoconfigure;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.restclient.RestTemplateBuilder;
 import org.springframework.stereotype.Service;
 import org.springframework.web.client.RestTemplate;
@@ -39,7 +41,7 @@ public class ExampleRestTemplateService {
 		return this.restTemplate;
 	}
 
-	public String test() {
+	public @Nullable String test() {
 		return this.restTemplate.getForEntity("/test", String.class).getBody();
 	}
 
diff --git a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/RestClientTestRestClientTwoComponentsIntegrationTests.java b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/RestClientTestRestClientTwoComponentsIntegrationTests.java
index befdf8ed000..58c3d754623 100644
--- a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/RestClientTestRestClientTwoComponentsIntegrationTests.java
+++ b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/RestClientTestRestClientTwoComponentsIntegrationTests.java
@@ -58,17 +58,17 @@ class RestClientTestRestClientTwoComponentsIntegrationTests {
 
 	@Test
 	void client1RestCallViaCustomizer() {
-		this.customizer.getServer(this.client1.getRestClientBuilder())
-			.expect(requestTo(uri("/test")))
-			.andRespond(withSuccess("hello", MediaType.TEXT_HTML));
+		MockRestServiceServer server = this.customizer.getServer(this.client1.getRestClientBuilder());
+		assertThat(server).isNotNull();
+		server.expect(requestTo(uri("/test"))).andRespond(withSuccess("hello", MediaType.TEXT_HTML));
 		assertThat(this.client1.test()).isEqualTo("hello");
 	}
 
 	@Test
 	void client2RestCallViaCustomizer() {
-		this.customizer.getServer(this.client2.getRestClientBuilder())
-			.expect(requestTo(uri("/test")))
-			.andRespond(withSuccess("there", MediaType.TEXT_HTML));
+		MockRestServiceServer server = this.customizer.getServer(this.client2.getRestClientBuilder());
+		assertThat(server).isNotNull();
+		server.expect(requestTo(uri("/test"))).andRespond(withSuccess("there", MediaType.TEXT_HTML));
 		assertThat(this.client2.test()).isEqualTo("there");
 	}
 
diff --git a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/RestClientTestRestTemplateTwoComponentsIntegrationTests.java b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/RestClientTestRestTemplateTwoComponentsIntegrationTests.java
index 2cd40bab55a..90543c70054 100644
--- a/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/RestClientTestRestTemplateTwoComponentsIntegrationTests.java
+++ b/module/spring-boot-restclient-test/src/test/java/org/springframework/boot/restclient/test/autoconfigure/RestClientTestRestTemplateTwoComponentsIntegrationTests.java
@@ -58,17 +58,17 @@ class RestClientTestRestTemplateTwoComponentsIntegrationTests {
 
 	@Test
 	void client1RestCallViaCustomizer() {
-		this.customizer.getServer(this.client1.getRestTemplate())
-			.expect(requestTo("/test"))
-			.andRespond(withSuccess("hello", MediaType.TEXT_HTML));
+		MockRestServiceServer server = this.customizer.getServer(this.client1.getRestTemplate());
+		assertThat(server).isNotNull();
+		server.expect(requestTo("/test")).andRespond(withSuccess("hello", MediaType.TEXT_HTML));
 		assertThat(this.client1.test()).isEqualTo("hello");
 	}
 
 	@Test
 	void client2RestCallViaCustomizer() {
-		this.customizer.getServer(this.client2.getRestTemplate())
-			.expect(requestTo("/test"))
-			.andRespond(withSuccess("there", MediaType.TEXT_HTML));
+		MockRestServiceServer server = this.customizer.getServer(this.client2.getRestTemplate());
+		assertThat(server).isNotNull();
+		server.expect(requestTo("/test")).andRespond(withSuccess("there", MediaType.TEXT_HTML));
 		assertThat(this.client2.test()).isEqualTo("there");
 	}