Add nullability annotations to tests in module/spring-boot-security-oauth2-authorization-server

See gh-47263

module/spring-boot-security-oauth2-authorization-server/build.gradle

@@ -39,3 +39,7 @@ dependencies {
 
 	testRuntimeOnly("ch.qos.logback:logback-classic")
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}

module/spring-boot-security-oauth2-authorization-server/src/test/java/org/springframework/boot/security/oauth2/server/authorization/autoconfigure/servlet/OAuth2AuthorizationServerWebSecurityConfigurationTests.java

@@ -19,6 +19,7 @@ package org.springframework.boot.security.oauth2.server.authorization.autoconfig
 import java.util.List;
 
 import jakarta.servlet.Filter;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.test.context.assertj.AssertableWebApplicationContext;
@@ -118,7 +119,7 @@ class OAuth2AuthorizationServerWebSecurityConfigurationTests {
 			});
 	}
 
-	private Filter findFilter(AssertableWebApplicationContext context, Class<? extends Filter> filter,
+	private @Nullable Filter findFilter(AssertableWebApplicationContext context, Class<? extends Filter> filter,
 			int filterChainIndex) {
 		FilterChainProxy filterChain = (FilterChainProxy) context.getBean(BeanIds.SPRING_SECURITY_FILTER_CHAIN);
 		List<SecurityFilterChain> filterChains = filterChain.getFilterChains();