Once connected within visualvm to a glassfish v3 instance (promoted build 62), trying to "start" a btrace script from the btrace tab triggers the following stacktrace after a couple of seconds :

java.lang.NullPointerException
at java.io.File.<init>(File.java:222)
at net.java.btrace.visualvm.impl.BTraceEngineImpl.findToolsJarPath(BTraceEngineImpl.java:301)
at net.java.btrace.visualvm.impl.BTraceEngineImpl.doStart(BTraceEngineImpl.java:138)
at net.java.btrace.visualvm.impl.BTraceEngineImpl.start(BTraceEngineImpl.java:104)
at net.java.btrace.visualvm.impl.BTraceTaskImpl.start(BTraceTaskImpl.java:183)
at net.java.btrace.visualvm.views.BTraceTaskEditorPanel.btnStartActionPerformed(BTraceTaskEditorPanel.java:351)
at net.java.btrace.visualvm.views.BTraceTaskEditorPanel.access$700(BTraceTaskEditorPanel.java:70)
at net.java.btrace.visualvm.views.BTraceTaskEditorPanel$5.actionPerformed(BTraceTaskEditorPanel.java:260)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6348)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6113)
at java.awt.Container.processEvent(Container.java:2085)
at java.awt.Component.dispatchEventImpl(Component.java:4714)
at java.awt.Container.dispatchEventImpl(Container.java:2143)
at java.awt.Component.dispatchEvent(Component.java:4544)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4618)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4282)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4212)
at java.awt.Container.dispatchEventImpl(Container.java:2129)
at java.awt.Window.dispatchEventImpl(Window.java:2475)
at java.awt.Component.dispatchEvent(Component.java:4544)
[catch] at java.awt.EventQueue.dispatchEvent(EventQueue.java:635)
at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

This is reproductible always, whatever the btrace script.
VisualVM is then stuck with the "Starting BTrace task..." message.