Destroyed objects trigger NullReferenceExceptions when loading a scene

[apaladeParticipant]

Hi there!

I’m seeing MissingReferenceException’s in FlowCanvas caused by what’s certainly an edge case for you. We apply some funky scene post-processing in our game that destroys a bunch of scene objects before entering play mode and then re-creates them after the the scene is loaded.

To clarify, we’re using the PostProcessScene attribute.

More info about the bug:

• Exception triggered in FlowCanvasModuleNodesVariablesGetVariable.cs at line 67. The blackboard variable’s value has been destroyed but it’s not a true null so the call to GetPrefabType fails.
• Happens in Node/FlowCanvas 2.8.5 but was seeing it in earlier versions as well
• Only triggered in the Editor when I have the FlowCanvas Window open.
• Only happens for Blackboard variables that point to scene objects that are destroyed as part of the scene post processing.

Full call stack attached. Error is fixed by adding a “fake-null” check in the if statement on line 62.

I’m on Node/FlowCanvas 2.8.5 and I’m getting NullRefs when I’m in the Editor, I have the FlowCanvas Window open and I start a scene

[GavalakisKeymaster]

Hello,

Ah, I see what is going on. Even if it’s a very special case, it’s nice to have everything cleaned up, so thanks for reporting this 🙂
If by “fake null” you mean something like that !value.value.Equals(null), then this is what I usually do to make sure that the UnityObject is truly null and what I just added in the GetVariable to avoid this problem.

Thanks for letting me know.

[apaladeParticipant]

Yeah, that’s what I meant by “fake null”. I figured it’s a real edge case for you but like you said – it’s nice to have everything tied up.

Thanks for a great pair of assets by the way! NodeCanvas and FlowCanvas are absolutely crucial for our game and we use them both extensively. I promise to send you an extensive feedback doc once the game is finally out and I have some time. 🙂

[GavalakisKeymaster]

Thanks! I am glad you like assets 🙂
Looking forward to your feedback and of course to see what game you are making with the assets!

[Author]

Posts