FULL PRODUCT VERSION :
>java -version
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
> ver
Microsoft Windows [Version 10.0.14393]


A DESCRIPTION OF THE PROBLEM :
It is possible to add a null value to a Stage's icon list. This raises a NullPointerException that is internally caught by the JavaFX API and never reaches the programmer's level. Later when attempting to make the stage visible, the application will crash with a InvocationTargetException (caused by a RuntimeException caused by a NullPointerException).

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Create a new JavaFX application.
In the start() method of the application's main class, add a null value to the Stage's icons list.
Make the stage visible.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
We should expect either of this result :

* Either an exception is raised immediately when attempting to insert the null value.

* Or the null value is ignored by the underlying stage code.
ACTUAL -
A NullPointerException is indeed raised by the JavaFX API but it is caught internally at line 164 of class com.sun.javafx.collections.ListListenerHelper<E>

Later when the Stage is made visible, another exception is raised.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
// 1st exception caugh internally by the JavaFX API.
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
finally
	at javafx.stage.Stage$4.onChanged(Stage.java:696)
	at com.sun.javafx.collections.TrackableObservableList.lambda$new$19(TrackableObservableList.java:45)
	at com.sun.javafx.collections.ListListenerHelper$SingleChange.fireValueChangedEvent(ListListenerHelper.java:164)
	at com.sun.javafx.collections.ListListenerHelper.fireValueChangedEvent(ListListenerHelper.java:73)
	at javafx.collections.ObservableListBase.fireChange(ObservableListBase.java:233)
	at javafx.collections.ListChangeBuilder.commit(ListChangeBuilder.java:482)
	at javafx.collections.ListChangeBuilder.endChange(ListChangeBuilder.java:541)
	at javafx.collections.ObservableListBase.endChange(ObservableListBase.java:205)
	at javafx.collections.ModifiableObservableListBase.add(ModifiableObservableListBase.java:155)
	at java.util.AbstractList.add(AbstractList.java:108)
	at stagenull.Main.start(Main.java:25)
	at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl.java:863)
	at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
	at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
	at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
	at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
	at java.lang.Thread.run(Thread.java:748)


// 2nd exception raised when attempting to make the stage visible
Exception in Application start method
java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
	at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
	at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
	at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException
	at javafx.stage.Stage.impl_visibleChanged(Stage.java:1189)
	at javafx.stage.Window$9.invalidated(Window.java:895)
	at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:109)
	at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:144)
	at javafx.stage.Window.setShowing(Window.java:922)
	at javafx.stage.Window.show(Window.java:937)
	at javafx.stage.Stage.show(Stage.java:259)
	at stagenull.Main.start(Main.java:33)
	at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl.java:863)
	at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
	at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
	at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
	at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
	... 1 more
Exception running application stagenull.Main

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
The following code makes the error happen all the time:

import javafx.application.Application;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) {
        try {
            System.out.println("start try");
            primaryStage.getIcons().add(null); // NullPointerException caught internally.
            System.out.println("end try");  // Always happen.
        } catch (Exception e) {
            System.out.println("error caught"); // Never happen.
        } finally {
            System.out.println("finally");
        }
        primaryStage.setTitle("Hello World!");
        primaryStage.show(); // InvocationTargetException <- RuntimeException <- NullPointerException
    }

    public static void main(String[] args) {
        launch(args);
    }
}


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

CUSTOMER SUBMITTED WORKAROUND :
Simply never insert a null value to the Stage's icon list. However as the error is not raised to the programmer's level it may be difficult to catch when resources such as icons are loaded programmatically.

So there should be 2 possible workaround for this bug:

* prevent null values from being added to the stage's icons list. The List interface does not prevent from addition null objects so in theory the null value is valid but on the other hand JavaFX has already this behavior when adding a null child to a parent. For example:

try {
    StackPane root = new StackPane();
    root.getChildren().add(null);
} catch (Exception e) {
     System.out.println("error caught"); // Happens all the time.
}

This code raises an InvocationTargetException (caused by a RuntimeException caused by a NullPointerException) immediately and it reach's the programmer's level. We could change the icon observable list in the Stage class to behave in a similar fashion.

* Or the handling of the icons' list should be modified to ignore null values completely. 
This would happen in JavaFX 8_131 at lines 696 and 1189 of the Stage class where, in both cases, the content of the list is being handled in order to get the peer native images.

Current unsafe code:

List<Object> platformImages = new ArrayList<Object>();
for (Image icon : icons) {
    platformImages.add(icon.impl_getPlatformImage());
}

Should become:

List<Object> platformImages = new ArrayList<Object>();
for (Image icon : icons) {
    if (icon == null) {
       continue;
    }
    platformImages.add(icon.impl_getPlatformImage());
}

Or by upgrading this code to JDK 8 streams and filter to prevent null values:

List<Object> platformImages = icons.stream()
                .filter(Objects::nonNull)
                .map(Image::impl_getPlatformImage)
                .collect(Collectors.toList());