NPE is JavaFX Task

[Peter Penzov]

Hi All,
    I have a question about a issue that I have with JavaFX Task. I'm using
the code from this example to display progress bar in TabPane when I click
on TreeView Node:

http://stackoverflow.com/questions/22803845/loading-logic-for-javafx-task

For some reason when I click multiple times on the node I get this
exception:


Exception in thread "JavaFX Application Thread"
java.lang.NullPointerException
        at com.sun.javafx.css.StyleManager.findMatchingStyles(Unknown
Source)
        at javafx.scene.CssStyleHelper.createStyleHelper(Unknown Source)
        at javafx.scene.Node.reapplyCss(Unknown Source)
        at javafx.scene.Node.impl_reapplyCSS(Unknown Source)
        at javafx.scene.Node.invalidatedScenes(Unknown Source)
        at javafx.scene.Node.setScenes(Unknown Source)
        at javafx.scene.Parent$1.onChanged(Unknown Source)
        at
com.sun.javafx.collections.TrackableObservableList.lambda$new$19(Unknown
Source)
        at
com.sun.javafx.collections.ListListenerHelper$Generic.fireValueChangedEvent(Unknown
Sourc
e)
        at
com.sun.javafx.collections.ListListenerHelper.fireValueChangedEvent(Unknown
Source)
        at javafx.collections.ObservableListBase.fireChange(Unknown Source)
        at javafx.collections.ListChangeBuilder.commit(Unknown Source)
        at javafx.collections.ListChangeBuilder.endChange(Unknown Source)
        at javafx.collections.ObservableListBase.endChange(Unknown Source)
        at javafx.collections.ModifiableObservableListBase.add(Unknown
Source)
        at java.util.AbstractList.add(Unknown Source)
        at com.sun.javafx.collections.VetoableListDecorator.add(Unknown
Source)
        at
com.sun.javafx.scene.control.skin.ProgressIndicatorSkin$IndeterminateSpinner.rebuild(Unkn
own Source)
        at
com.sun.javafx.scene.control.skin.ProgressIndicatorSkin$IndeterminateSpinner.access$400(U
nknown Source)
        at
com.sun.javafx.scene.control.skin.ProgressIndicatorSkin$2.invalidated(Unknown
Source)
        at javafx.beans.property.IntegerPropertyBase.markInvalid(Unknown
Source)
        at javafx.beans.property.IntegerPropertyBase.set(Unknown Source)
        at javafx.css.StyleableIntegerProperty.set(Unknown Source)
        at javafx.beans.property.IntegerProperty.setValue(Unknown Source)
        at javafx.css.StyleableIntegerProperty.applyStyle(Unknown Source)
        at javafx.css.StyleableIntegerProperty.applyStyle(Unknown Source)
        at javafx.scene.CssStyleHelper.transitionToState(Unknown Source)
        at javafx.scene.Node.impl_processCSS(Unknown Source)
        at javafx.scene.Parent.impl_processCSS(Unknown Source)
        at javafx.scene.control.Control.impl_processCSS(Unknown Source)
        at javafx.scene.Parent.impl_processCSS(Unknown Source)
        at javafx.scene.Parent.impl_processCSS(Unknown Source)
        at javafx.scene.Node.processCSS(Unknown Source)
        at javafx.scene.Node.processCSS(Unknown Source)
        at javafx.scene.Node.processCSS(Unknown Source)
        at javafx.scene.Node.processCSS(Unknown Source)
        at javafx.scene.Node.processCSS(Unknown Source)
        at javafx.scene.Node.processCSS(Unknown Source)
        at javafx.scene.Scene.doCSSPass(Unknown Source)
        at javafx.scene.Scene.access$3600(Unknown Source)
        at javafx.scene.Scene$ScenePulseListener.pulse(Unknown Source)
        at com.sun.javafx.tk.Toolkit.lambda$runPulse$31(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.javafx.tk.Toolkit.runPulse(Unknown Source)
        at com.sun.javafx.tk.Toolkit.firePulse(Unknown Source)
        at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(Unknown Source)
        at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(Unknown Source)
        at
com.sun.javafx.tk.quantum.QuantumToolkit.lambda$runToolkit$401(Unknown
Source)
        at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.lambda$null$146(Unknown
Source)
        at java.lang.Thread.run(Unknown Source)


Can you advice me is this JavaFX issue or the code that I'm using is
incorrect?

BR,
Peter

ref
http://stackoverflow.com/questions/22803845/loading-logic-for-javafx-task