java version "1.5.0-beta"
Java(TM) 2 Runtime Environment, Standard Edition 
(build 1.5.0-beta-b32c)
Java HotSpot(TM) Client VM (build 1.5.0-beta-
b32c, mixed mode)

For an unknown reason NPE (see bellow) was 
thrown when:
- Changing any properties of any object is 
throwing the NPE (see bellow).
- Trying to save changes.

I closed the file (and form editor) then 
reopened. This fixed the problem.

The problem was reproduced twice with 
ColorPicker sample program.

Here is the stack trace:

java.lang.NullPointerException
	at 
org.netbeans.modules.form.JavaCodeGenerator.gener
ateListenerAddCode(JavaCodeGenerator.java:1429)
	at 
org.netbeans.modules.form.JavaCodeGenerator.gener
ateComponentEvents(JavaCodeGenerator.java:1412)
	at 
org.netbeans.modules.form.JavaCodeGenerator.addIn
itCode(JavaCodeGenerator.java:899)
	at 
org.netbeans.modules.form.JavaCodeGenerator.regen
erateInitComponents(JavaCodeGenerator.java:734)
	at 
org.netbeans.modules.form.JavaCodeGenerator.acces
s$900(JavaCodeGenerator.java:46)
	at 
org.netbeans.modules.form.JavaCodeGenerator$FormL
istener.formChanged(JavaCodeGenerator.java:2546)
	at 
org.netbeans.modules.form.FormModel.fireEvents
(FormModel.java:821)
[catch] at 
org.netbeans.modules.form.FormModel$EventBroker.r
un(FormModel.java:892)
	at 
java.awt.event.InvocationEvent.dispatch
(InvocationEvent.java:201)
	at java.awt.EventQueue.dispatchEvent
(EventQueue.java:461)
	at 
java.awt.EventDispatchThread.pumpOneEventForHiera
rchy(EventDispatchThread.java:234)
	at 
java.awt.EventDispatchThread.pumpEventsForHierarc
hy(EventDispatchThread.java:163)
	at 
java.awt.EventDispatchThread.pumpEvents
(EventDispatchThread.java:157)
	at 
java.awt.EventDispatchThread.pumpEvents
(EventDispatchThread.java:149)
	at java.awt.EventDispatchThread.run
(EventDispatchThread.java:110)