[WICKET-7173] JavaxWebSocketConfigurator: Add back null check for httpSession (#1356)

Changes for WICKET-7162 removed a null check, leading to another NPE when trying to add httpSession to the userProperties map

Author: weber-semedy

wicket-native-websocket/wicket-native-websocket-javax/src/main/java/org/apache/wicket/protocol/ws/javax/WicketServerEndpointConfig.java

@@ -143,13 +143,15 @@ public void modifyHandshake(ServerEndpointConfig sec, HandshakeRequest request,
 
 			Object httpSession = request.getHttpSession();
 			LOG.trace("httpSession: {}", httpSession);
-			userProperties.put(JavaxUpgradeHttpRequest.SESSION, httpSession);
-			if (httpSession instanceof HttpSession)
+			if (httpSession != null)
 			{
-				userProperties.put(JavaxUpgradeHttpRequest.CONTEXT_PATH,((HttpSession)httpSession).getServletContext().getContextPath());
+				userProperties.put(JavaxUpgradeHttpRequest.SESSION, httpSession);
+				if (httpSession instanceof HttpSession)
+				{
+					userProperties.put(JavaxUpgradeHttpRequest.CONTEXT_PATH,((HttpSession)httpSession).getServletContext().getContextPath());
+				}
 			}
 
-
 			Map<String, List<String>> headers = request.getHeaders();
 			LOG.trace("headers: {}", headers);
 			if (headers != null)