Add nullability annotations to tests in module/spring-boot-data-jpa

See gh-47263

module/spring-boot-data-jpa/build.gradle

@@ -49,3 +49,7 @@ dependencies {
 	testRuntimeOnly("com.zaxxer:HikariCP")
 	testRuntimeOnly("jakarta.servlet:jakarta.servlet-api")
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}

module/spring-boot-data-jpa/src/test/java/org/springframework/boot/data/jpa/autoconfigure/AbstractDataJpaRepositoriesAutoConfigurationTests.java

@@ -149,7 +149,9 @@ abstract class AbstractDataJpaRepositoriesAutoConfigurationTests {
 
 	@SuppressWarnings("unchecked")
 	private Map<Metamodel, JpaMetamodel> jpaMetamodelCache() {
-		return (Map<Metamodel, JpaMetamodel>) ReflectionTestUtils.getField(JpaMetamodel.class, "CACHE");
+		Object field = ReflectionTestUtils.getField(JpaMetamodel.class, "CACHE");
+		assertThat(field).isNotNull();
+		return (Map<Metamodel, JpaMetamodel>) field;
 	}
 
 	@Configuration(proxyBeanMethods = false)