NullReferenceException in GraphOwnerInspector.OnDestroy

[erikParticipant]

Hey,
I get this error when I have the Canvas open during play and destroy the scene of which the FSM owner is part of.
It’s not fatal or anything, just annoying. 😉

NullReferenceException: Object reference not set to an instance of an object
NodeCanvas.Editor.GraphOwnerInspector.OnDestroy () (at Assets/ParadoxNotion/CanvasCore/Framework/Design/Editor/Inspectors/GraphOwnerInspector.cs:42)

Looking at the code it’s quite obvious…

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void OnDestroy(){ if (owner == null && owner.graph != null){ if (owner.graphIsBound){ Undo.DestroyObjectImmediate(owner.graph); } } }

[GavalakisKeymaster]

Hey,

Yeah, This is actually a hacky line of code there, which “works” in editor due to how unity objects handle null operators.
I will have fix this in a more proper way.
Thanks 🙂

[sugoidevParticipant]

Maybe I misunderstood your reply, but I think the reported issue is that this

if (owner == null && owner.graph != null){

will always throw depending on the order Unity destroys the object.
It will try to evaluate owner.graph when owner is null.
The fix is to use

if (owner != null && owner.graph != null){

so owner.graph is touched when owner is not null.

[psykawParticipant]

The right fix is:

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void OnDestroy(){ if (owner == null && !ReferenceEquals(owner, null) && owner.graph != null){ if (owner.graphIsBound){ Undo.DestroyObjectImmediate(owner.graph); } } }

If owner equals to null (could have been destroyed but is not null) so you check if owner is really null with ReferenceEquals and if not continue.

[sugoidevParticipant]

If it is fake-null (when owner == null is true, but ReferenceEquals(owner, null) isn’t), won’t accessing its members throw with message “The object of type TYPE has been destroyed but you are still trying to access it.”?

[GavalakisKeymaster]

What I do there is very hacky, but considering that the hack is kept, then @psykaw’s code is the “correct” fix. Truth is that the whole OnDestroy method there is not really mandatory, since the object will be cleaned up anyway, but is rather a mini-convenience cleanup, which is not critical at all.
@sugoidev, if ‘ReferenceEquals(owner, null) == false’, then the ‘owner.graph’ will of course not be accessed 🙂

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