Improve null-safety of module/spring-boot-web-server

See gh-47263

module/spring-boot-jetty/src/main/java/org/springframework/boot/jetty/servlet/JettyServletWebServerFactory.java

@@ -89,6 +89,7 @@ import org.springframework.boot.web.server.servlet.ServletWebServerSettings;
 import org.springframework.boot.web.servlet.ServletContextInitializer;
 import org.springframework.context.ResourceLoaderAware;
 import org.springframework.core.io.ResourceLoader;
+import org.springframework.lang.Contract;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.CollectionUtils;
@@ -263,6 +264,7 @@ public class JettyServletWebServerFactory extends JettyWebServerFactory
 		}
 	}
 
+	@Contract("null -> true")
 	private boolean isNegative(@Nullable Duration sessionTimeout) {
 		return sessionTimeout == null || sessionTimeout.isNegative();
 	}

module/spring-boot-session-data-mongodb/src/dockerTest/java/org/springframework/boot/session/data/mongodb/autoconfigure/SessionDataMongoAutoConfigurationTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.session.data.mongodb.autoconfigure;
 
 import java.time.Duration;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.testcontainers.containers.MongoDBContainer;
@@ -90,7 +91,7 @@ class SessionDataMongoAutoConfigurationTests extends AbstractSessionAutoConfigur
 	}
 
 	private ContextConsumer<AssertableWebApplicationContext> validateSpringSessionUsesMongo(String collectionName,
-			Duration timeout) {
+			@Nullable Duration timeout) {
 		return (context) -> {
 			MongoIndexedSessionRepository repository = validateSessionRepository(context,
 					MongoIndexedSessionRepository.class);

module/spring-boot-tomcat/src/main/java/org/springframework/boot/tomcat/servlet/TomcatServletWebServerFactory.java

@@ -85,6 +85,7 @@ import org.springframework.boot.web.server.servlet.ServletWebServerSettings;
 import org.springframework.boot.web.servlet.ServletContextInitializer;
 import org.springframework.context.ResourceLoaderAware;
 import org.springframework.core.io.ResourceLoader;
+import org.springframework.lang.Contract;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.CollectionUtils;
@@ -382,6 +383,7 @@ public class TomcatServletWebServerFactory extends TomcatWebServerFactory
 		return Math.max(sessionTimeout.toMinutes(), 1);
 	}
 
+	@Contract("null -> true")
 	private boolean isZeroOrLess(@Nullable Duration sessionTimeout) {
 		return sessionTimeout == null || sessionTimeout.isNegative() || sessionTimeout.isZero();
 	}

module/spring-boot-web-server/src/main/java/org/springframework/boot/web/server/servlet/Session.java

@@ -41,7 +41,7 @@ public class Session {
 	 * Session timeout. If a duration suffix is not specified, seconds will be used.
 	 */
 	@DurationUnit(ChronoUnit.SECONDS)
-	private Duration timeout = Duration.ofMinutes(30);
+	private @Nullable Duration timeout = Duration.ofMinutes(30);
 
 	/**
 	 * Session tracking modes.
@@ -63,11 +63,11 @@ public class Session {
 
 	private final SessionStoreDirectory sessionStoreDirectory = new SessionStoreDirectory();
 
-	public Duration getTimeout() {
+	public @Nullable Duration getTimeout() {
 		return this.timeout;
 	}
 
-	public void setTimeout(Duration timeout) {
+	public void setTimeout(@Nullable Duration timeout) {
 		this.timeout = timeout;
 	}