Revert "WICKET-5049 Wicket Session may be null in SessionBindingListener after deserialization"

This reverts commit a46f50fb57fec92994425b1e0a3466a4aa624a09.
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 44e2a9c..30c49ba 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
@@ -438,11 +438,8 @@
 				log.debug("Session unbound: " + sessionId);
 			}
 
-			if (wicketSession != null)
-			{
-				wicketSession.onInvalidate();
-			}
-			
+			wicketSession.onInvalidate();
+
 			Application application = Application.get(applicationKey);
 			if (application == null)
 			{