Index: trunk/autoquest-core-usability-evaluation/src/main/java/de/ugoe/cs/autoquest/usability/util/NullNode.java
===================================================================
--- trunk/autoquest-core-usability-evaluation/src/main/java/de/ugoe/cs/autoquest/usability/util/NullNode.java	(revision 1164)
+++ trunk/autoquest-core-usability-evaluation/src/main/java/de/ugoe/cs/autoquest/usability/util/NullNode.java	(revision 1173)
@@ -15,10 +15,8 @@
 package de.ugoe.cs.autoquest.usability.util;
 
-import java.util.Collections;
-import java.util.List;
-
 import org.apache.commons.lang.StringUtils;
 
 import de.ugoe.cs.autoquest.tasktrees.treeifc.ITask;
+import de.ugoe.cs.autoquest.tasktrees.treeifc.ITaskVisitor;
 
 /**
@@ -31,4 +29,15 @@
 public class NullNode implements ITask {
 
+	
+	/**
+	 * 
+	 */
+	private static final long serialVersionUID = -3325477932754494485L;
+
+	@Override
+	public int getId() {
+		return 0;
+	}
+	
     /* (non-Javadoc)
      * @see de.ugoe.cs.autoquest.tasktrees.treeifc.ITaskTreeNode#getName()
@@ -63,5 +72,5 @@
      * @see de.ugoe.cs.autoquest.tasktrees.treeifc.ITaskTreeNode#accept(de.ugoe.cs.autoquest.tasktrees.treeifc.NodeVisitor)
      */
-    public void accept(NodeVisitor visitor) {
+    public void accept(ITaskVisitor visitor) {
         
     }