FULL PRODUCT VERSION :
java version "1.6.0_02"
Java(TM) SE Runtime Environment (build 1.6.0_02-b06)
Java HotSpot(TM) Client VM (build 1.6.0_02-b06, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
A postorder enumeration returned by DefaultMutableTreeNode will return null from nextElement() instead of throwing an exception after hasMoreElements() returns false.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Create a tree of one or more DefaultMutableTreeNode objects, create a postorder enumeration of the elements by calling postorderEnumeration() (or depthFirstEnumeration() , which does the same thing). Exhaust the enumeration by calling nextElement(). Then call nextElement() again.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
After hasMoreElements() returns false, calling nextElement() should throw a NoSuchElementException exception.
ACTUAL -
nextElement() returns null if there are no more elements.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.Enumeration;
import java.util.NoSuchElementException;
import javax.swing.tree.DefaultMutableTreeNode;

public class TreeTest {

    public TreeTest() {
        DefaultMutableTreeNode root = new DefaultMutableTreeNode("root");
        root.add(new DefaultMutableTreeNode("child"));
        Enumeration enum_ = root.depthFirstEnumeration();
        while (enum_.hasMoreElements()) {
            System.out.println(enum_.nextElement().toString());
        }
        try {
            Object obj = enum_.nextElement();
        } catch (NoSuchElementException e) {
            System.out.println("Exception thrown");
            e.printStackTrace();
        }
        System.out.println("Exception NOT thrown!!!!!");
    }
    
    public static void main(String[] args) {
        TreeTest app = new TreeTest();
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Avoid writing code that relies on nextElement() throwing an exception.