Fix NullPointerException when creating cursor with null device #2414

This is a follow-up to e8aadbb which
introduced a regression when working with null devices.

If null is passed as argument, the value of Device.getDevice() is used
as a fallback when initializing this field. This field must be used for
all other operations in the constructor, rather than the constructor
argument.

Closes #2414

Author: ptziegler

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/Cursor.java

@@ -119,7 +119,7 @@ public final class Cursor extends Resource {
 public Cursor(Device device, int style) {
 	super(device);
 	this.cursorHandleProvider = new StyleCursorHandleProvider(style);
-	this.handle = this.cursorHandleProvider.createHandle(device, DEFAULT_ZOOM).getHandle();
+	this.handle = this.cursorHandleProvider.createHandle(this.device, DEFAULT_ZOOM).getHandle();
 	init();
 	this.device.registerResourceWithZoomSupport(this);
 }
@@ -160,7 +160,7 @@ public Cursor(Device device, int style) {
 public Cursor(Device device, ImageData source, ImageData mask, int hotspotX, int hotspotY) {
 	super(device);
 	this.cursorHandleProvider = new ImageDataWithMaskCursorHandleProvider(source, mask, hotspotX, hotspotY);
-	this.handle = this.cursorHandleProvider.createHandle(device, DEFAULT_ZOOM).getHandle();
+	this.handle = this.cursorHandleProvider.createHandle(this.device, DEFAULT_ZOOM).getHandle();
 	init();
 	this.device.registerResourceWithZoomSupport(this);
 }
@@ -229,7 +229,7 @@ private static CursorHandle setupCursorFromImageData(ImageData source, ImageData
 public Cursor(Device device, ImageData source, int hotspotX, int hotspotY) {
 	super(device);
 	this.cursorHandleProvider = new ImageDataCursorHandleProvider(source, hotspotX, hotspotY);
-	this.handle = this.cursorHandleProvider.createHandle(device, DEFAULT_ZOOM).getHandle();
+	this.handle = this.cursorHandleProvider.createHandle(this.device, DEFAULT_ZOOM).getHandle();
 	init();
 	this.device.registerResourceWithZoomSupport(this);
 }
@@ -341,7 +341,7 @@ public Cursor(Device device, ImageDataProvider imageDataProvider, int hotspotX,
 	super(device);
 	if (imageDataProvider == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
 	this.cursorHandleProvider = new ImageDataProviderCursorHandleProvider(imageDataProvider, hotspotX, hotspotY);
-	this.handle = this.cursorHandleProvider.createHandle(device, DEFAULT_ZOOM).getHandle();
+	this.handle = this.cursorHandleProvider.createHandle(this.device, DEFAULT_ZOOM).getHandle();
 	init();
 	this.device.registerResourceWithZoomSupport(this);
 }

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_graphics_Cursor.java

@@ -154,6 +154,8 @@ public void test_ConstructorWithImageDataProvider() {
 	Image sourceImage = new Image(display, 10, 10);
 	Cursor cursor = new Cursor(display, sourceImage::getImageData, 0, 0);
 	cursor.dispose();
+	cursor = new Cursor(null, sourceImage::getImageData, 0, 0);
+	cursor.dispose();
 	sourceImage.dispose();
 
 	assertThrows("No exception thrown when ImageDataProvider is null",