Handle null RSocketServer address when setting port property

See gh-23084

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/rsocket/context/RSocketPortInfoApplicationContextInitializer.java

@@ -63,7 +63,9 @@ public class RSocketPortInfoApplicationContextInitializer
 
 		@Override
 		public void onApplicationEvent(RSocketServerInitializedEvent event) {
-			setPortProperty(this.applicationContext, event.getServer().address().getPort());
+			if (event.getServer().address() != null) {
+				setPortProperty(this.applicationContext, event.getServer().address().getPort());
+			}
 		}
 
 		private void setPortProperty(ApplicationContext context, int port) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/rsocket/context/RSocketPortInfoApplicationContextInitializerTests.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2012-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.boot.rsocket.context;
+
+import java.net.InetSocketAddress;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.rsocket.server.RSocketServer;
+import org.springframework.boot.rsocket.server.RSocketServerException;
+import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+@ExtendWith(SpringExtension.class)
+public class RSocketPortInfoApplicationContextInitializerTests {
+
+	@Autowired
+	private RSocketPortInfoApplicationContextInitializer initializer;
+
+	@Autowired
+	private ConfigurableApplicationContext context;
+
+	@Autowired
+	private ApplicationEventPublisher publisher;
+
+	@Test
+	void nullAddressDoesNotThrow() {
+		initializer.initialize(context);
+		publisher.publishEvent(new RSocketServerInitializedEvent(new RSocketServer() {
+			@Override
+			public void start() throws RSocketServerException {
+
+			}
+
+			@Override
+			public void stop() throws RSocketServerException {
+
+			}
+
+			@Override
+			public InetSocketAddress address() {
+				return null;
+			}
+		}));
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class Config {
+
+		@Bean
+		public RSocketPortInfoApplicationContextInitializer rSocketPortInfoApplicationContextInitializer() {
+			return new RSocketPortInfoApplicationContextInitializer();
+		}
+	}
+}