Fix regression due to incorrect optional use

chatto/src/main/java/org/ros/chatto/controller/Home.java

@@ -26,7 +26,7 @@ public class Home {
 
 	@RequestMapping("/")
 	public String showPage(Model model, Principal principal) {
-		final String welcomeMessage = Optional.of(principal).map(p -> {
+		final String welcomeMessage = Optional.ofNullable(principal).map(p -> {
 			return String.format("Welcome back %s!", p.getName());
 		}).orElse("Welcome to chatto");
 		model.addAttribute("message", welcomeMessage);