During shutdown, tomcat crashes as follows:

SEVERE: Exception sending context destroyed event to listener instance of class org.apache.tomcat.websocket.server.WsContextListener
java.lang.NullPointerException
        at org.apache.catalina.core.StandardContext.listenerStop(StandardContext.java:5076)
        at org.apache.catalina.core.StandardContext.stopInternal(StandardContext.java:5719)
        at org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:232)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:160)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:649)
        at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:672)
        at org.apache.catalina.startup.HostConfig$DeployDescriptor.run(HostConfig.java:1859)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
        at java.util.concurrent.FutureTask.run(FutureTask.java:262)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)


An analysis of the code shows that getInstanceManager() is being called, and an assumption is made that this call will always return not-null, which is not the case. The rest of the code shows that there are valid situations where this returns null.

5075 	try {
5076 	getInstanceManager().destroyInstance(listeners[j]);
5077 	} catch (Throwable t) {
5078 	t = ExceptionUtils.unwrapInvocationTargetException(t);
5079 	ExceptionUtils.handleThrowable(t);
5080 	getLogger().error
5081 	(sm.getString("standardContext.listenerStop",
5082 	listeners[j].getClass().getName()), t);
5083 	ok = false;
5084 	} 

The fix should be a simple null check on or around line 5076.