We appear to have one class that causes the groovy code completion plugin to NPE, details from the eclipse error log below:

The 'Groovy Code Completions' proposal computer from the 'org.codehaus.groovy.eclipse.codeassist.completion' plug-in did not complete normally. The extension has thrown a runtime exception.

java.lang.NullPointerException
at org.codehaus.groovy.eclipse.codeassist.processors.LocalVariableCompletionProcessor.createClosureProposals(LocalVariableCompletionProcessor.java:82)
at org.codehaus.groovy.eclipse.codeassist.processors.LocalVariableCompletionProcessor.generateProposals(LocalVariableCompletionProcessor.java:73)
at org.codehaus.groovy.eclipse.codeassist.requestor.GroovyCompletionProposalComputer.computeCompletionProposals(GroovyCompletionProposalComputer.java:162)
at org.eclipse.jdt.internal.ui.text.java.CompletionProposalComputerDescriptor.computeCompletionProposals(CompletionProposalComputerDescriptor.java:333)
at org.eclipse.jdt.internal.ui.text.java.CompletionProposalCategory.computeCompletionProposals(CompletionProposalCategory.java:337)
at org.eclipse.jdt.internal.ui.text.java.ContentAssistProcessor.collectProposals(ContentAssistProcessor.java:325)
at org.eclipse.jdt.internal.ui.text.java.ContentAssistProcessor.computeCompletionProposals(ContentAssistProcessor.java:282)
at org.eclipse.jface.text.contentassist.ContentAssistant.computeCompletionProposals(ContentAssistant.java:1839)
at org.eclipse.jface.text.contentassist.CompletionProposalPopup.computeProposals(CompletionProposalPopup.java:566)
at org.eclipse.jface.text.contentassist.CompletionProposalPopup.access$16(CompletionProposalPopup.java:563)
at org.eclipse.jface.text.contentassist.CompletionProposalPopup$2.run(CompletionProposalPopup.java:498)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.jface.text.contentassist.CompletionProposalPopup.showProposals(CompletionProposalPopup.java:492)
at org.eclipse.jface.text.contentassist.ContentAssistant.showPossibleCompletions(ContentAssistant.java:1665)
at org.eclipse.jdt.internal.ui.javaeditor.CompilationUnitEditor$AdaptedSourceViewer.doOperation(CompilationUnitEditor.java:183)
at org.eclipse.ui.texteditor.ContentAssistAction$1.run(ContentAssistAction.java:82)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ui.texteditor.ContentAssistAction.run(ContentAssistAction.java:80)
at org.eclipse.jface.action.Action.runWithEvent(Action.java:499)
at org.eclipse.jface.commands.ActionHandler.execute(ActionHandler.java:119)
at org.eclipse.ui.internal.handlers.E4HandlerProxy.execute(E4HandlerProxy.java:90)
at sun.reflect.GeneratedMethodAccessor31.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:56)
at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:243)
at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:224)
at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:132)
at org.eclipse.e4.core.commands.internal.HandlerServiceHandler.execute(HandlerServiceHandler.java:167)
at org.eclipse.core.commands.Command.executeWithChecks(Command.java:499)
at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:508)
at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:213)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.executeCommand(KeyBindingDispatcher.java:285)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.press(KeyBindingDispatcher.java:504)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.processKeyEvent(KeyBindingDispatcher.java:555)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.filterKeySequenceBindings(KeyBindingDispatcher.java:376)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.access$0(KeyBindingDispatcher.java:322)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher$KeyDownFilter.handleEvent(KeyBindingDispatcher.java:84)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.filterEvent(Display.java:1262)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1056)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1081)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1066)
at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1108)
at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1104)
at org.eclipse.swt.widgets.Widget.wmChar(Widget.java:1525)
at org.eclipse.swt.widgets.Control.WM_CHAR(Control.java:4723)
at org.eclipse.swt.widgets.Canvas.WM_CHAR(Canvas.java:344)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4611)
at org.eclipse.swt.widgets.Canvas.windowProc(Canvas.java:340)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:4977)
at org.eclipse.swt.internal.win32.OS.DispatchMessageW(Native Method)
at org.eclipse.swt.internal.win32.OS.DispatchMessage(OS.java:2549)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3757)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1113)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:997)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:138)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:610)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:567)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:124)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:354)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:181)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:636)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:591)
at org.eclipse.equinox.launcher.Main.run(Main.java:1450)
at org.eclipse.equinox.launcher.Main.main(Main.java:1426)

eclipse.buildId=3.4.0.201310051614-RELEASE-e43
java.version=1.7.0_51
java.vendor=Oracle Corporation
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=en_GB
Framework arguments: -product org.springsource.sts.ide
Command-line arguments: -os win32 -ws win32 -arch x86_64 -product org.springsource.sts.ide

If this has been raised in the wrong place feel free to close/move etc.