Formatting produce errors instead of formatting

I want to trying out the formatting feature. But this doesn't work. Instead there is an exception:

java.lang.VerifyError: (class: org/codehaus/groovy/eclipse/refactoring/core/utils/astScanner/RefactoringCodeVisitorSupport, method: visitClosureListExpression signature: (Lorg/codehaus/groovy/ast/expr/ClosureListExpression;)V) Incompatible argument to function
at org.codehaus.groovy.eclipse.refactoring.formatter.GroovyBeautifier.combineClosures(GroovyBeautifier.java:57)
at org.codehaus.groovy.eclipse.refactoring.formatter.GroovyBeautifier.getBeautifiEdits(GroovyBeautifier.java:50)
at org.codehaus.groovy.eclipse.refactoring.formatter.DefaultGroovyFormatter.format(DefaultGroovyFormatter.java:134)
at org.codehaus.groovy.eclipse.refactoring.popup.actions.FormatAction.doAction(FormatAction.java:37)
at org.codehaus.groovy.eclipse.editor.actions.EditingAction.run(EditingAction.java:45)
at org.eclipse.ui.internal.PluginAction.runWithEvent(PluginAction.java:251)
at org.eclipse.ui.commands.ActionHandler.execute(ActionHandler.java:185)
at org.eclipse.ui.internal.handlers.LegacyHandlerWrapper.execute(LegacyHandlerWrapper.java:109)
at org.eclipse.core.commands.Command.executeWithChecks(Command.java:476)
at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:508)
at org.eclipse.ui.internal.handlers.HandlerService.executeCommand(HandlerService.java:169)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard.executeCommand(WorkbenchKeyboard.java:472)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard.press(WorkbenchKeyboard.java:824)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard.processKeyEvent(WorkbenchKeyboard.java:882)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard.filterKeySequenceBindings(WorkbenchKeyboard.java:571)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard.access$3(WorkbenchKeyboard.java:512)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard$KeyDownFilter.handleEvent(WorkbenchKeyboard.java:127)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.filterEvent(Display.java:1184)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1002)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1027)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1012)
at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1040)
at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1036)
at org.eclipse.swt.widgets.Widget.wmChar(Widget.java:1352)
at org.eclipse.swt.widgets.Control.WM_CHAR(Control.java:3894)
at org.eclipse.swt.widgets.Canvas.WM_CHAR(Canvas.java:341)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:3787)
at org.eclipse.swt.widgets.Canvas.windowProc(Canvas.java:337)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:4528)
at org.eclipse.swt.internal.win32.OS.DispatchMessageW(Native Method)
at org.eclipse.swt.internal.win32.OS.DispatchMessage(OS.java:2371)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3420)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2382)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2346)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2198)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:493)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:288)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:488)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:113)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:193)
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:386)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:549)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:504)
at org.eclipse.equinox.launcher.Main.run(Main.java:1236)
at org.eclipse.equinox.launcher.Main.main(Main.java:1212)

The code i want to format is:

/**
 * 
 */
package de.kamann.groovy.v157



/**
 * @author thorsten
 *
 */
class FormatterDemo{
String method(){
	
}
	
	
}