diff --git a/src/main/java/org/gcube/portlets/user/td/widgetcommonevent/client/type/ExpressionType.java b/src/main/java/org/gcube/portlets/user/td/widgetcommonevent/client/type/ExpressionType.java
index bfbf003..b390340 100644
--- a/src/main/java/org/gcube/portlets/user/td/widgetcommonevent/client/type/ExpressionType.java
+++ b/src/main/java/org/gcube/portlets/user/td/widgetcommonevent/client/type/ExpressionType.java
@@ -4,10 +4,12 @@
 package org.gcube.portlets.user.td.widgetcommonevent.client.type;
 
 /**
- * @author Francesco Mangiacrapa francesco.mangiacrapa@isti.cnr.it
- * @Dec 9, 2013
+ * 
+ * @author "Giancarlo Panichi" 
+ * <a href="mailto:g.panichi@isti.cnr.it">g.panichi@isti.cnr.it</a> 
  *
  */
 public enum ExpressionType {
-	CREATECOLUMNEXPRESSION;
+	CREATECOLUMNEXPRESSION,
+	EXPRESSIONNULL;
 }