Sporadic NPE in ZeroWidthCharactersLineContentCodeMiningProvider

[ptziegler]

This exception is sporadically logged in our test suite where we open and close the Java code editor in rapid succession.

Exception in thread "org.eclipse.jdt.internal.ui.text.JavaReconciler" java.lang.NullPointerException: Cannot invoke "org.eclipse.jface.preference.IPreferenceStore.getBoolean(String)" because "this.store" is null
	at org.eclipse.ui.internal.texteditor.codemining.ZeroWidthCharactersLineContentCodeMiningProvider.readShowZwspFromStore(ZeroWidthCharactersLineContentCodeMiningProvider.java:114)
	at org.eclipse.ui.internal.texteditor.codemining.ZeroWidthCharactersLineContentCodeMiningProvider.loadStoreAndReadProperty(ZeroWidthCharactersLineContentCodeMiningProvider.java:105)
	at org.eclipse.ui.internal.texteditor.codemining.ZeroWidthCharactersLineContentCodeMiningProvider.provideCodeMinings(ZeroWidthCharactersLineContentCodeMiningProvider.java:60)
	at org.eclipse.jface.internal.text.codemining.CodeMiningManager.lambda$3(CodeMiningManager.java:203)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:214)
	at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:1024)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:570)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:560)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:265)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:723)
	at org.eclipse.jface.internal.text.codemining.CodeMiningManager.getCodeMinings(CodeMiningManager.java:209)
	at org.eclipse.jface.internal.text.codemining.CodeMiningManager.updateCodeMinings(CodeMiningManager.java:150)
	at org.eclipse.jface.internal.text.codemining.CodeMiningManager.run(CodeMiningManager.java:139)
	at org.eclipse.jface.text.source.SourceViewer.updateCodeMinings(SourceViewer.java:1378)
	at org.eclipse.jdt.internal.ui.javaeditor.JavaCodeMiningReconciler.reconciled(JavaCodeMiningReconciler.java:57)
	at org.eclipse.jdt.internal.ui.javaeditor.CompilationUnitEditor.reconciled(CompilationUnitEditor.java:1676)
	at org.eclipse.jdt.internal.ui.text.java.JavaReconcilingStrategy.reconciled(JavaReconcilingStrategy.java:228)
	at org.eclipse.jdt.internal.ui.text.JavaCompositeReconcilingStrategy.reconciled(JavaCompositeReconcilingStrategy.java:171)
	at org.eclipse.jdt.internal.ui.text.JavaCompositeReconcilingStrategy.reconcile(JavaCompositeReconcilingStrategy.java:115)
	at org.eclipse.jface.text.reconciler.MonoReconciler.process(MonoReconciler.java:77)
	at org.eclipse.jface.text.reconciler.AbstractReconciler$BackgroundWorker.run(AbstractReconciler.java:203)
	at java.base/java.lang.Thread.run(Thread.java:1474)

As far as I can tell, the store can only be null when the code-mining provider has been disposed. The provider is usually disposed in the UI thread. But at that point, there might still be a pending request, which then operates on an invalid provider.