JettyWebSocketSession.getRemoteAddress throws IllegalArgumentException on a erroring-out session in 5.3.x versions

[Spikhalskiy]

We have some custom observability code added to Web Socket Connection lifecycle.
The following exception happens when we try to call getRemoteAddress() on an erroring-out and closing session.

java.lang.IllegalArgumentException: Object of class [null] must be an instance of class java.net.InetSocketAddress
	at org.springframework.util.Assert.instanceCheckFailed(Assert.java:702) ~[spring-core-5.3.25.jar:5.3.25]
	at org.springframework.util.Assert.isInstanceOf(Assert.java:602) ~[spring-core-5.3.25.jar:5.3.25]
	at org.springframework.util.Assert.isInstanceOf(Assert.java:633) ~[spring-core-5.3.25.jar:5.3.25]
	at org.springframework.web.socket.adapter.jetty.JettyWebSocketSession$Jetty10SessionHelper.getRemoteAddress(JettyWebSocketSession.java:351) ~[spring-websocket-5.3.25.jar:5.3.25]
	at org.springframework.web.socket.adapter.jetty.JettyWebSocketSession.getRemoteAddress(JettyWebSocketSession.java:153) ~[spring-websocket-5.3.25.jar:5.3.25]
	at <our custom handler, that calls session.getRemoteAddress()> 
	at org.springframework.web.socket.handler.WebSocketHandlerDecorator.handleTransportError(WebSocketHandlerDecorator.java:80) ~[spring-websocket-5.3.25.jar:5.3.25]
	at org.springframework.web.socket.handler.LoggingWebSocketHandlerDecorator.handleTransportError(LoggingWebSocketHandlerDecorator.java:64) ~[spring-websocket-5.3.25.jar:5.3.25]
	at org.springframework.web.socket.handler.ExceptionWebSocketHandlerDecorator.handleTransportError(ExceptionWebSocketHandlerDecorator.java:68) ~[spring-websocket-5.3.25.jar:5.3.25]
	at org.springframework.web.socket.adapter.jetty.Jetty10WebSocketHandlerAdapter.onWebSocketError(Jetty10WebSocketHandlerAdapter.java:130) ~[spring-websocket-5.3.25.jar:5.3.25]
	at org.eclipse.jetty.websocket.common.JettyWebSocketFrameHandler.onError(JettyWebSocketFrameHandler.java:260) ~[websocket-jetty-common-10.0.14.jar:10.0.14]
	at org.eclipse.jetty.websocket.core.internal.WebSocketCoreSession.lambda$closeConnection$2(WebSocketCoreSession.java:284) ~[websocket-core-common-10.0.14.jar:10.0.14]
	at org.eclipse.jetty.server.handler.ContextHandler.handle(ContextHandler.java:1470) ~[jetty-server-10.0.14.jar:10.0.14]
	at org.eclipse.jetty.server.handler.ContextHandler.handle(ContextHandler.java:1489) ~[jetty-server-10.0.14.jar:10.0.14]
	at org.eclipse.jetty.websocket.core.server.internal.AbstractHandshaker$1.handle(AbstractHandshaker.java:212) ~[websocket-core-server-10.0.14.jar:10.0.14]
	at org.eclipse.jetty.websocket.core.internal.WebSocketCoreSession.closeConnection(WebSocketCoreSession.java:284) ~[websocket-core-common-10.0.14.jar:10.0.14]
	at org.eclipse.jetty.websocket.core.internal.WebSocketCoreSession.onEof(WebSocketCoreSession.java:254) ~[websocket-core-common-10.0.14.jar:10.0.14]
	at org.eclipse.jetty.websocket.core.internal.WebSocketConnection.onClose(WebSocketConnection.java:221) ~[websocket-core-common-10.0.14.jar:10.0.14]
	at org.eclipse.jetty.io.SelectorManager.connectionClosed(SelectorManager.java:330) ~[jetty-io-10.0.14.jar:10.0.14]

Expected

It's clearly not an intended behavior of getRemoteAddress method to throw on null here, especially taking into account that WebSocketSession#getRemoteAddress is explicitly marked an @Nullable

Environment

Spring 5.3.x and Jetty 10
This doesn't reproduce on Spring 5.2.x and 6+.

[bclozel]

Spring Framework 5.3.x is out of open source support so we won't be releasing new versions for this generation on Maven Central.

See https://spring.io/projects/spring-framework#support