I just had the same problem and this is what the stack trace looks like... I couldn't get more info at the moment.
java.lang.NullPointerException: Cannot invoke "org.openide.filesystems.FileObject.getAttribute(String)" because "fo" is null at org.openide.filesystems.FileUtil.toFile(FileUtil.java:813) at org.openide.filesystems.FileUtil.getFileDisplayName(FileUtil.java:1574) at org.netbeans.modules.java.hints.spiimpl.batch.BatchSearch$2.run(BatchSearch.java:279) at org.netbeans.modules.java.hints.spiimpl.batch.BatchSearch$2.run(BatchSearch.java:240) at org.netbeans.modules.java.source.parsing.MimeTask.run(MimeTask.java:60) at org.netbeans.modules.parsing.impl.TaskProcessor.callUserTask(TaskProcessor.java:586) at org.netbeans.modules.parsing.api.ParserManager$MimeTaskAction.run(ParserManager.java:364) at org.netbeans.modules.parsing.api.ParserManager$MimeTaskAction.run(ParserManager.java:347) at org.netbeans.modules.parsing.impl.TaskProcessor$2.call(TaskProcessor.java:181) at org.netbeans.modules.parsing.impl.TaskProcessor$2.call(TaskProcessor.java:178) at org.netbeans.modules.masterfs.filebasedfs.utils.FileChangedManager.priorityIO(FileChangedManager.java:153) at org.netbeans.modules.masterfs.providers.ProvidedExtensions.priorityIO(ProvidedExtensions.java:335) at org.netbeans.modules.parsing.nb.DataObjectEnvFactory.runPriorityIO(DataObjectEnvFactory.java:118) at org.netbeans.modules.parsing.impl.Utilities.runPriorityIO(Utilities.java:67) at org.netbeans.modules.parsing.impl.TaskProcessor.runUserTask(TaskProcessor.java:178) at org.netbeans.modules.parsing.api.ParserManager.parse(ParserManager.java:318) at org.netbeans.api.java.source.JavaSource.runUserActionTaskImpl(JavaSource.java:433) at org.netbeans.api.java.source.JavaSource.runUserActionTask(JavaSource.java:425) at org.netbeans.modules.java.hints.spiimpl.batch.BatchSearch.getLocalVerifiedSpans(BatchSearch.java:240) at org.netbeans.modules.java.hints.spiimpl.batch.BatchSearch.access$400(BatchSearch.java:76) at org.netbeans.modules.java.hints.spiimpl.batch.BatchSearch$LocalIndexEnquirer.validateResource(BatchSearch.java:550) at org.netbeans.modules.java.hints.spiimpl.batch.BatchSearch.getVerifiedSpans(BatchSearch.java:183) at org.netbeans.modules.java.hints.spiimpl.batch.BatchUtilities.applyFixes(BatchUtilities.java:174) at org.netbeans.modules.java.hints.onsave.RemoveUnusedAfterSave.performTask(RemoveUnusedAfterSave.java:85) at org.netbeans.modules.editor.lib.BeforeSaveTasks$TaskRunnable$1.run(BeforeSaveTasks.java:148) at org.netbeans.editor.GuardedDocument.runAtomicAsUser(GuardedDocument.java:333) at org.netbeans.modules.editor.lib.BeforeSaveTasks$TaskRunnable.run(BeforeSaveTasks.java:131) at org.netbeans.modules.editor.lib.TrailingWhitespaceRemove.runLocked(TrailingWhitespaceRemove.java:77) at org.netbeans.modules.editor.lib.BeforeSaveTasks$TaskRunnable.run(BeforeSaveTasks.java:128) at org.netbeans.modules.editor.impl.ReformatBeforeSaveTask.runLocked(ReformatBeforeSaveTask.java:101) at org.netbeans.modules.editor.lib.BeforeSaveTasks$TaskRunnable.run(BeforeSaveTasks.java:128) at org.netbeans.modules.java.hints.onsave.RemoveUnusedAfterSave$1.run(RemoveUnusedAfterSave.java:98) at org.netbeans.modules.java.hints.onsave.RemoveUnusedAfterSave$1.run(RemoveUnusedAfterSave.java:96) at org.netbeans.api.java.source.JavaSource$MultiTask.run(JavaSource.java:504) at org.netbeans.modules.parsing.impl.TaskProcessor.callUserTask(TaskProcessor.java:586) at org.netbeans.modules.parsing.api.ParserManager$UserTaskAction.run(ParserManager.java:132) at org.netbeans.modules.parsing.api.ParserManager$UserTaskAction.run(ParserManager.java:116) at org.netbeans.modules.parsing.impl.TaskProcessor$2.call(TaskProcessor.java:181) at org.netbeans.modules.parsing.impl.TaskProcessor$2.call(TaskProcessor.java:178) at org.netbeans.modules.masterfs.filebasedfs.utils.FileChangedManager.priorityIO(FileChangedManager.java:153) at org.netbeans.modules.masterfs.providers.ProvidedExtensions.priorityIO(ProvidedExtensions.java:335) at org.netbeans.modules.parsing.nb.DataObjectEnvFactory.runPriorityIO(DataObjectEnvFactory.java:118) at org.netbeans.modules.parsing.impl.Utilities.runPriorityIO(Utilities.java:67) at org.netbeans.modules.parsing.impl.TaskProcessor.runUserTask(TaskProcessor.java:178) at org.netbeans.modules.parsing.api.ParserManager.parse(ParserManager.java:83) at org.netbeans.api.java.source.JavaSource.runUserActionTaskImpl(JavaSource.java:454) at org.netbeans.api.java.source.JavaSource.runUserActionTask(JavaSource.java:425) at org.netbeans.modules.java.hints.onsave.RemoveUnusedAfterSave.runLocked(RemoveUnusedAfterSave.java:96) at org.netbeans.modules.editor.lib.BeforeSaveTasks$TaskRunnable.run(BeforeSaveTasks.java:128) at org.netbeans.modules.editor.lib.BeforeSaveTasks.runTasks(BeforeSaveTasks.java:105) at org.netbeans.modules.editor.lib.BeforeSaveTasks$2.run(BeforeSaveTasks.java:86) at org.openide.text.CloneableEditorSupport.saveDocumentImpl(CloneableEditorSupport.java:729) at org.openide.text.CloneableEditorSupport.saveDocument(CloneableEditorSupport.java:620) at org.openide.text.DataEditorSupport.superSaveDoc(DataEditorSupport.java:572) at org.openide.text.DataEditorSupport$SaveImpl.run(DataEditorSupport.java:1332) at org.openide.filesystems.EventControl.runAtomicAction(EventControl.java:102) at org.openide.filesystems.FileSystem.runAtomicAction(FileSystem.java:494) at org.openide.filesystems.FileUtil.runAtomicAction(FileUtil.java:402) at org.openide.text.DataEditorSupport.saveDocument(DataEditorSupport.java:568) at org.netbeans.modules.openide.loaders.SimpleES$SaveCookieImpl.save(SimpleES.java:202) at org.openide.actions.SaveAction.performAction(SaveAction.java:107) at org.openide.actions.SaveAction.performAction(SaveAction.java:77) at org.openide.actions.SaveAction$Delegate.actionPerformed(SaveAction.java:224) at org.openide.awt.ContextAction$Performer.actionPerformed(ContextAction.java:446) at org.openide.awt.ContextManager.actionPerformed(ContextManager.java:263) at org.openide.awt.ContextAction.actionPerformed(ContextAction.java:106) at org.openide.util.actions.ActionInvoker$1.run(ActionInvoker.java:68) at org.openide.util.actions.ActionInvoker$ActionRunnable.actionPerformed(ActionInvoker.java:137) at org.netbeans.core.ModuleActions.invokeAction(ModuleActions.java:84) at org.netbeans.modules.openide.actions.ActionsBridgeImpl.invokeAction(ActionsBridgeImpl.java:35) at org.openide.util.actions.ActionInvoker$ActionRunnable.doRun(ActionInvoker.java:128) at org.openide.util.actions.ActionInvoker$2.run(ActionInvoker.java:85) at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1418) at org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:45) at org.openide.util.lookup.Lookups.executeWith(Lookups.java:278) [catch] at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2033)
