Add nullability annotations to tests in module/spring-boot-graphql-test

See gh-47263

module/spring-boot-graphql-test/build.gradle

@@ -48,3 +48,7 @@ dependencies {
 	testRuntimeOnly("ch.qos.logback:logback-classic")
 	testRuntimeOnly("tools.jackson.core:jackson-databind")
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}

module/spring-boot-graphql-test/src/test/java/org/springframework/boot/graphql/test/autoconfigure/Book.java

@@ -18,15 +18,19 @@ package org.springframework.boot.graphql.test.autoconfigure;
 
 public class Book {
 
+	@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) {

module/spring-boot-graphql-test/src/test/java/org/springframework/boot/graphql/test/autoconfigure/GraphQlTypeExcludeFilterTests.java

@@ -192,7 +192,7 @@ class GraphQlTypeExcludeFilterTests {
 
 		@Override
 		public Mono<WebGraphQlResponse> intercept(WebGraphQlRequest request, Chain chain) {
-			return null;
+			return Mono.empty();
 		}
 
 	}
@@ -206,7 +206,7 @@ class GraphQlTypeExcludeFilterTests {
 
 		@Override
 		public Mono<List<GraphQLError>> resolveException(Throwable exception, DataFetchingEnvironment environment) {
-			return null;
+			return Mono.empty();
 		}
 
 	}