diff --git a/module/spring-boot-graphql/build.gradle b/module/spring-boot-graphql/build.gradle
index 021d2865a6d..2034744222b 100644
--- a/module/spring-boot-graphql/build.gradle
+++ b/module/spring-boot-graphql/build.gradle
@@ -54,5 +54,11 @@ dependencies {
 	testImplementation("org.springframework.graphql:spring-graphql-test")
 	testImplementation("org.springframework.security:spring-security-test")
 
+	testCompileOnly("com.google.code.findbugs:jsr305")
+
 	testRuntimeOnly("ch.qos.logback:logback-classic")
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}
diff --git a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/Book.java b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/Book.java
index 3648005fe8b..51a7b70893c 100644
--- a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/Book.java
+++ b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/Book.java
@@ -26,15 +26,19 @@ import org.springframework.data.annotation.Id;
 public class Book {
 
 	@Id
+	@SuppressWarnings("NullAway.Init")
 	String id;
 
+	@SuppressWarnings("NullAway.Init")
 	String name;
 
+	@SuppressWarnings("NullAway.Init")
 	int pageCount;
 
+	@SuppressWarnings("NullAway.Init")
 	String author;
 
-	public Book() {
+	protected Book() {
 	}
 
 	public Book(String id, String name, int pageCount, String author) {
diff --git a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/DefaultGraphQlSchemaConditionTests.java b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/DefaultGraphQlSchemaConditionTests.java
index 3dd6ebb780e..259ea8e0098 100644
--- a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/DefaultGraphQlSchemaConditionTests.java
+++ b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/DefaultGraphQlSchemaConditionTests.java
@@ -18,6 +18,7 @@ package org.springframework.boot.graphql.autoconfigure;
 
 import java.util.Collection;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.autoconfigure.condition.ConditionEvaluationReport;
@@ -78,7 +79,7 @@ class DefaultGraphQlSchemaConditionTests {
 		assertThat(context.getBean("success")).isEqualTo("success");
 	}
 
-	private String conditionReportMessage(AssertableApplicationContext context) {
+	private @Nullable String conditionReportMessage(AssertableApplicationContext context) {
 		Collection<ConditionEvaluationReport.ConditionAndOutcomes> conditionAndOutcomes = ConditionEvaluationReport
 			.get(context.getSourceApplicationContext().getBeanFactory())
 			.getConditionAndOutcomesBySource()
diff --git a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/GraphQlTestDataFetchers.java b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/GraphQlTestDataFetchers.java
index 9dd190d00c2..6062af81721 100644
--- a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/GraphQlTestDataFetchers.java
+++ b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/GraphQlTestDataFetchers.java
@@ -20,8 +20,11 @@ import java.util.Arrays;
 import java.util.List;
 
 import graphql.schema.DataFetcher;
+import org.jspecify.annotations.Nullable;
 import reactor.core.publisher.Flux;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 /**
  * Test utility class holding {@link DataFetcher} implementations.
  *
@@ -39,14 +42,22 @@ public final class GraphQlTestDataFetchers {
 	}
 
 	public static DataFetcher<Book> getBookByIdDataFetcher() {
-		return (environment) -> getBookById(environment.getArgument("id"));
+		return (environment) -> {
+			String id = environment.getArgument("id");
+			assertThat(id).isNotNull();
+			return getBookById(id);
+		};
 	}
 
 	public static DataFetcher<Flux<Book>> getBooksOnSaleDataFetcher() {
-		return (environment) -> getBooksOnSale(environment.getArgument("minPages"));
+		return (environment) -> {
+			Integer minPages = environment.getArgument("minPages");
+			assertThat(minPages).isNotNull();
+			return getBooksOnSale(minPages);
+		};
 	}
 
-	public static Book getBookById(String id) {
+	public static @Nullable Book getBookById(String id) {
 		return books.stream().filter((book) -> book.getId().equals(id)).findFirst().orElse(null);
 	}
 
diff --git a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/reactive/GraphQlWebFluxAutoConfigurationTests.java b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/reactive/GraphQlWebFluxAutoConfigurationTests.java
index 489107b7897..f29a9eb2ca0 100644
--- a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/reactive/GraphQlWebFluxAutoConfigurationTests.java
+++ b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/reactive/GraphQlWebFluxAutoConfigurationTests.java
@@ -23,6 +23,7 @@ import java.util.function.Consumer;
 
 import graphql.schema.idl.TypeRuntimeWiring;
 import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Mono;
 
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.predicate.RuntimeHintsPredicates;
@@ -354,13 +355,13 @@ class GraphQlWebFluxAutoConfigurationTests {
 		@Bean
 		@Order(-1)
 		RouterFunction<?> before() {
-			return (r) -> null;
+			return (r) -> Mono.empty();
 		}
 
 		@Bean
 		@Order(1)
 		RouterFunction<?> after() {
-			return (r) -> null;
+			return (r) -> Mono.empty();
 		}
 
 	}
diff --git a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/security/GraphQlWebFluxSecurityAutoConfigurationTests.java b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/security/GraphQlWebFluxSecurityAutoConfigurationTests.java
index c0c5948ede3..431d35f2659 100644
--- a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/security/GraphQlWebFluxSecurityAutoConfigurationTests.java
+++ b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/security/GraphQlWebFluxSecurityAutoConfigurationTests.java
@@ -153,8 +153,11 @@ class GraphQlWebFluxSecurityAutoConfigurationTests {
 
 		@Bean
 		RuntimeWiringConfigurer bookDataFetcher(BookService bookService) {
-			return (builder) -> builder.type(TypeRuntimeWiring.newTypeWiring("Query")
-				.dataFetcher("bookById", (env) -> bookService.getBookdById(env.getArgument("id"))));
+			return (builder) -> builder.type(TypeRuntimeWiring.newTypeWiring("Query").dataFetcher("bookById", (env) -> {
+				String id = env.getArgument("id");
+				assertThat(id).isNotNull();
+				return bookService.getBookdById(id);
+			}));
 		}
 
 		@Bean
diff --git a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/security/GraphQlWebMvcSecurityAutoConfigurationTests.java b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/security/GraphQlWebMvcSecurityAutoConfigurationTests.java
index 13126e4deaf..1ea419e85ef 100644
--- a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/security/GraphQlWebMvcSecurityAutoConfigurationTests.java
+++ b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/security/GraphQlWebMvcSecurityAutoConfigurationTests.java
@@ -18,6 +18,7 @@ package org.springframework.boot.graphql.autoconfigure.security;
 
 import graphql.schema.idl.TypeRuntimeWiring;
 import org.assertj.core.api.ThrowingConsumer;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.autoconfigure.AutoConfigurations;
@@ -142,8 +143,11 @@ class GraphQlWebMvcSecurityAutoConfigurationTests {
 
 		@Bean
 		RuntimeWiringConfigurer bookDataFetcher(BookService bookService) {
-			return (builder) -> builder.type(TypeRuntimeWiring.newTypeWiring("Query")
-				.dataFetcher("bookById", (env) -> bookService.getBookdById(env.getArgument("id"))));
+			return (builder) -> builder.type(TypeRuntimeWiring.newTypeWiring("Query").dataFetcher("bookById", (env) -> {
+				String id = env.getArgument("id");
+				assertThat(id).isNotNull();
+				return bookService.getBookdById(id);
+			}));
 		}
 
 		@Bean
@@ -156,7 +160,7 @@ class GraphQlWebMvcSecurityAutoConfigurationTests {
 	static class BookService {
 
 		@PreAuthorize("hasRole('USER')")
-		Book getBookdById(String id) {
+		@Nullable Book getBookdById(String id) {
 			return GraphQlTestDataFetchers.getBookById(id);
 		}
 
diff --git a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/servlet/GraphQlWebMvcAutoConfigurationTests.java b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/servlet/GraphQlWebMvcAutoConfigurationTests.java
index 609d7f5c2c3..940ddf07ea4 100644
--- a/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/servlet/GraphQlWebMvcAutoConfigurationTests.java
+++ b/module/spring-boot-graphql/src/test/java/org/springframework/boot/graphql/autoconfigure/servlet/GraphQlWebMvcAutoConfigurationTests.java
@@ -18,6 +18,7 @@ package org.springframework.boot.graphql.autoconfigure.servlet;
 
 import java.time.Duration;
 import java.util.Map;
+import java.util.Optional;
 
 import graphql.schema.idl.TypeRuntimeWiring;
 import org.assertj.core.api.ThrowingConsumer;
@@ -313,13 +314,13 @@ class GraphQlWebMvcAutoConfigurationTests {
 		@Bean
 		@Order(-1)
 		RouterFunction<?> before() {
-			return (r) -> null;
+			return (r) -> Optional.empty();
 		}
 
 		@Bean
 		@Order(1)
 		RouterFunction<?> after() {
-			return (r) -> null;
+			return (r) -> Optional.empty();
 		}
 
 	}