Plugin prevents IDEA from shutting down

It is related to https://youtrack.jetbrains.com/issue/IDEA-314162/NPE-in-TextEditorImpl.toString-during-shutdown-caused-by-com.intellij.openapi.util.ObjectNodeassertNoChildren-is-preventing but the underlying reason is probably that some `Disposable` is not propably disposed.

I think the bug appeared in some later IDEA version, it is reproducible with 2022.3.2 and 2023.1 EAP.