java.lang.NullPointerException: Cannot invoke "org.eclipse.gef.mvc.fx.parts.IContentPart.getRoot()" because "part" is null

[catinhat44]

Hi, so i closed the previous issue as the main problem was actually resolved and opened this one for the follow-up question. I am really sorry to bother you again but I've been stuck with it for a VERY long time, I do not know at all how to proceed and I really need to make this thing work. So i hope that someone could help me.

When i start an eclipse plugin (part 5 of the tutorial) and try to add a new node, this is what i keep getting:

java.lang.NullPointerException: Cannot invoke "org.eclipse.gef.mvc.fx.parts.IContentPart.getRoot()" because "part" is null
	at org.eclipse.gef.mvc.fx.policies.CreationPolicy.createFocusOperation(CreationPolicy.java:217)
	at org.eclipse.gef.mvc.fx.policies.CreationPolicy.create(CreationPolicy.java:152)
	at org.eclipse.gef.mvc.fx.policies.CreationPolicy.create(CreationPolicy.java:201)
	at com.itemis.gef.tutorial.mindmap.policies.CreateNewNodeOnClickHandler.click(CreateNewNodeOnClickHandler.java:85)
	at org.eclipse.gef.mvc.fx.gestures.ClickDragGesture.press(ClickDragGesture.java:351)
	at org.eclipse.gef.mvc.fx.gestures.ClickDragGesture$1.handle(ClickDragGesture.java:100)
	at org.eclipse.gef.mvc.fx.gestures.ClickDragGesture$1.handle(ClickDragGesture.java:1)
	at javafx.base@19/com.sun.javafx.event.CompositeEventHandler$NormalEventFilterRecord.handleCapturingEvent(CompositeEventHandler.java:321)
	at javafx.base@19/com.sun.javafx.event.CompositeEventHandler.dispatchCapturingEvent(CompositeEventHandler.java:98)
	at javafx.base@19/com.sun.javafx.event.EventHandlerManager.dispatchCapturingEvent(EventHandlerManager.java:221)
	at javafx.base@19/com.sun.javafx.event.EventHandlerManager.dispatchCapturingEvent(EventHandlerManager.java:180)
	at javafx.base@19/com.sun.javafx.event.CompositeEventDispatcher.dispatchCapturingEvent(CompositeEventDispatcher.java:43)
	at javafx.base@19/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:52)
	at org.eclipse.gef.fx.swt.canvas.FXCanvasEx$EventDispatcherEx.dispatchEvent(FXCanvasEx.java:155)
	at javafx.base@19/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at javafx.base@19/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at javafx.base@19/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at javafx.base@19/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
	at javafx.base@19/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
	at javafx.base@19/javafx.event.Event.fireEvent(Event.java:198)
	at javafx.graphics@19/javafx.scene.Scene$MouseHandler.process(Scene.java:3894)
	at javafx.graphics@19/javafx.scene.Scene.processMouseEvent(Scene.java:1887)
	at javafx.graphics@19/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2620)
	at javafx.graphics@19/com.sun.javafx.tk.quantum.EmbeddedScene.lambda$mouseEvent$4(EmbeddedScene.java:289)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
	at javafx.graphics@19/com.sun.javafx.tk.quantum.EmbeddedScene.lambda$mouseEvent$5(EmbeddedScene.java:282)
	at javafx.graphics@19/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:457)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
	at javafx.graphics@19/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:456)
	at org.eclipse.swt.internal.win32.OS.DispatchMessage(Native Method)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3643)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1155)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1046)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:155)
	at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:643)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:550)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:171)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:152)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:203)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:136)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:402)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:255)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:578)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:659)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:596)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1467)
	at org.eclipse.equinox.launcher.Main.main(Main.java:1440)

What I figured out till now:

1. SimpleMindMapApplication works smoothly in both cases: with an empty SimpleMindMap at launch AND when using createComplexExample() to populate a starting mindmap.
2. SimpleMindMapPlugin fails in both cases mentioned above. Thus, i have a suspicion that the problem is a transition from JavaFX application to Exlipse plugin.
3. The problem (probably) comes from the following part of code:
   • addContentChild() in an AbstractContentPart class does this operation at the very end: contentChildren.setAll(newContentChildren);
   • in case of SimpleMindMapApplication after performing this action, new element is also added to the contentPartMap (which is a property of the InfiniteCanvasViewer). in case of SimpleMindMapPlugin it DOES NOT happen, thus, new element is not added to the contentPartMap.
   • afterwards CreationPolicy class tries to retrieve new element with IContentPart<? extends Node> contentPart = viewer.getContentPartMap().get(content);. For the SimpleMindMapApplication it works fine, while SimpleMindMapPlugin returns null because an element was not added to contentPartMap before. Later ITransactionalOperation focusOperation = createFocusOperation(contentPart); throws an exception mentioned above because of contentPart being null. However, i cannot add any null check here because it is a library code.

The same happens when trying to create a new connection between nodes: SimpleMindMapApplication works, SimpleMindMapPlugin fails.

So the question is: why do they behave differently? I cannot see any place in the plugin code where you have to set some dependencies of the contentPartMap in the InfiniteCanvasViewer. Since it works fine for the SimpleMindMapApplication I do not see any other possible source of error except the SimpleMindMapEditor.
Does anyone have hints/workarounds/advices for this issue?

UPD: removing nodes fails in plugin too. Is there any specific reason why everything works well for SimpleMindMapApplication but some stuff fails for SimpleMindMapPlugin? E.g. incompatibility of newer gef versions with the tutorial code or something similar?

Thank you very much in advance!