WICKET-5049 Wicket Session may be null in SessionBindingListener after deserialization
diff --git a/wicket-core/src/main/java/org/apache/wicket/session/HttpSessionStore.java b/wicket-core/src/main/java/org/apache/wicket/session/HttpSessionStore.java
index 30c49ba..44e2a9c 100644
--- a/wicket-core/src/main/java/org/apache/wicket/session/HttpSessionStore.java
+++ b/wicket-core/src/main/java/org/apache/wicket/session/HttpSessionStore.java
@@ -438,8 +438,11 @@
 				log.debug("Session unbound: " + sessionId);
 			}
 
-			wicketSession.onInvalidate();
-
+			if (wicketSession != null)
+			{
+				wicketSession.onInvalidate();
+			}
+			
 			Application application = Application.get(applicationKey);
 			if (application == null)
 			{