Add nullability annotations to tests in module/spring-boot-reactor

See gh-47263

module/spring-boot-reactor/build.gradle

@@ -34,5 +34,11 @@ dependencies {
 	testImplementation(project(":test-support:spring-boot-test-support"))
 	testImplementation("io.micrometer:context-propagation")
 
+	testCompileOnly("com.google.code.findbugs:jsr305")
+
 	testRuntimeOnly("ch.qos.logback:logback-classic")
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}

module/spring-boot-reactor/src/test/java/org/springframework/boot/reactor/ReactorEnvironmentPostProcessorTests.java

@@ -24,6 +24,7 @@ import org.junit.jupiter.api.condition.JRE;
 import reactor.core.Scannable;
 import reactor.core.publisher.Flux;
 
+import org.springframework.boot.SpringApplication;
 import org.springframework.mock.env.MockEnvironment;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -41,7 +42,7 @@ class ReactorEnvironmentPostProcessorTests {
 		MockEnvironment environment = new MockEnvironment();
 		environment.setProperty("spring.threads.virtual.enabled", "true");
 		ReactorEnvironmentPostProcessor postProcessor = new ReactorEnvironmentPostProcessor();
-		postProcessor.postProcessEnvironment(environment, null);
+		postProcessor.postProcessEnvironment(environment, new SpringApplication());
 	}
 
 	@Test