RFR: 6603771: Nimbus L&F: Ctrl+F7 keybinding for Jinternal Frame throws a NPE.

[Sergey Bylokhov]

On Fri, 9 Dec 2022 08:06:43 GMT, Prasanta Sadhukhan <psadhukhan at openjdk.org> wrote:

> In Swingset2 JInternalFrame demo, focusing on any internalframes and pressing Ctrl+F7 and then any of up/down/left/arrow key to move the internal frames results in NPE in NimbusL&F.
> It is because `JComponent.processKeyBinding() `calls `SwingUtilities.notifyAction` which calls `BasicDesktopPaneUI.actionPerformed` where it gets `Desktop.minOnScreenInsets` property to get the Insets and then uses insets.top/bottom/left/right value to move the internalframe but this property is not defined for Nimbus so deferencing Insets object results in NPE.
> 
> Fix is added to create a 0 insets incase some L&F do not define` Desktop.minOnScreenInsets` property.
> No regression test is added as it can be easily checked by SwingSet2 JInternalFrame demo.

It would be good to add a test case to make sure this bug will not happen someday again.

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PR: https://git.openjdk.org/jdk/pull/11605