diff --git a/src/main/java/org/gcube/portlets/user/td/widgetcommonevent/shared/expression/C_Expression.java b/src/main/java/org/gcube/portlets/user/td/widgetcommonevent/shared/expression/C_Expression.java
index ddbe10f..ceb61c4 100644
--- a/src/main/java/org/gcube/portlets/user/td/widgetcommonevent/shared/expression/C_Expression.java
+++ b/src/main/java/org/gcube/portlets/user/td/widgetcommonevent/shared/expression/C_Expression.java
@@ -2,13 +2,17 @@ package org.gcube.portlets.user.td.widgetcommonevent.shared.expression;
 
 import java.io.Serializable;
 
-public class C_Expression implements Serializable{
+public class C_Expression implements Serializable {
 
 	
 	private static final long serialVersionUID = 7818512507606450235L;
 	
 	protected String id="Expression";
 
+	public C_Expression(){
+		
+	}
+	
 	public String getId() {
 		return id;
 	}