org.netbeans.mdr.util.DebugException: Invalid key
	at org.netbeans.mdr.storagemodel.MdrStorage.getObjectsFromIndex(MdrStorage.java:725)
	at org.netbeans.mdr.storagemodel.IndexImmutSet.getObjects(IndexImmutSet.java:66)
	at org.netbeans.mdr.storagemodel.AssocEndIndexSet.iterator(AssocEndIndexSet.java:96)
	at org.netbeans.mdr.handlers.AEIndexSetWrapper.iterator(AEIndexSetWrapper.java:186)
	at org.netbeans.modules.refactoring.plugins.WhereUsedQueryPlugin.prepare(WhereUsedQueryPlugin.java:94)
	at org.netbeans.modules.refactoring.api.AbstractRefactoring.pluginsPrepare(AbstractRefactoring.java:274)
	at org.netbeans.modules.refactoring.api.AbstractRefactoring.prepare(AbstractRefactoring.java:140)
	at org.netbeans.modules.refactoring.experimental.plugins.SafeDeleteRefactoringPlugin.prepare(SafeDeleteRefactoringPlugin.java:80)
	at org.netbeans.modules.refactoring.api.AbstractRefactoring.pluginsPrepare(AbstractRefactoring.java:274)
	at org.netbeans.modules.refactoring.api.AbstractRefactoring.prepare(AbstractRefactoring.java:140)
	at org.netbeans.modules.refactoring.spi.ui.ParametersPanel$Prepare.run(ParametersPanel.java:675)
	at org.openide.util.Task.run(Task.java:207)
	at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:469)
[catch] at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:870)