NPE on WebSocketServerContainerInitializer.configureContext(ServletContextHandler)

[joakime]

If the ServletContextHandler isn't added to the Server yet, and you use WebSocketServerContainerInitializer.configureContext(context) like this ...

        Server server = new Server(8080);

        HandlerList handlers = new HandlerList();

        ServletContextHandler context = new ServletContextHandler(
                ServletContextHandler.SESSIONS);
        context.setContextPath("/");
        handlers.addHandler(context);

        // Enable javax.websocket configuration for the context
        ServerContainer wsContainer = WebSocketServerContainerInitializer.configureContext(context);

        // Add your websockets to the container
        wsContainer.addEndpoint(EchoJsrSocket.class);

        handlers.addHandler(new DefaultHandler());

        server.setHandler(handlers);
        server.start();

You'll get a NPE

Exception in thread "main" java.lang.NullPointerException
	at org.eclipse.jetty.websocket.jsr356.server.deploy.WebSocketServerContainerInitializer.configureContext(WebSocketServerContainerInitializer.java:148)
	at org.eclipse.jetty.embedded.WebSocketJsrServer.main(WebSocketJsrServer.java:63)