Reproducible with latest mustang build on all platforms.
When a dialog is set with null modality type and shown, the following exception is thrown:

Exception in thread "main" java.lang.NullPointerException
        at java.awt.ModalEventFilter.createFilterForDialog(ModalEventFilter.java:104)
        at java.awt.Dialog.show(Dialog.java:1023)
        at java.awt.Component.show(Component.java:1406)
        at java.awt.Component.setVisible(Component.java:1359)
        at java.awt.Window.setVisible(Window.java:573)
        at java.awt.Dialog.setVisible(Dialog.java:961)

To reproduce:
Run the attached testcase