CDK Sever monitoring 'Add...' button throws exception

org.eclipse.core.runtime.AssertionFailedException: null argument:
	at org.eclipse.core.runtime.Assert.isNotNull(Assert.java:85)
	at org.eclipse.core.runtime.Assert.isNotNull(Assert.java:73)
	at org.eclipse.jface.viewers.StructuredViewer.assertElementsNotNull(StructuredViewer.java:585)
	at org.eclipse.jface.viewers.StructuredViewer.getRawChildren(StructuredViewer.java:996)
	at org.eclipse.jface.viewers.ColumnViewer.getRawChildren(ColumnViewer.java:701)
	at org.eclipse.jface.viewers.AbstractTableViewer.getRawChildren(AbstractTableViewer.java:1035)
	at org.eclipse.jface.viewers.StructuredViewer.getFilteredChildren(StructuredViewer.java:901)
	at org.eclipse.jface.viewers.StructuredViewer.getSortedChildren(StructuredViewer.java:1078)
	at org.eclipse.jface.viewers.AbstractTableViewer.internalRefreshAll(AbstractTableViewer.java:664)
	at org.eclipse.jface.viewers.AbstractTableViewer.internalRefresh(AbstractTableViewer.java:612)
	at org.eclipse.jface.viewers.AbstractTableViewer.internalRefresh(AbstractTableViewer.java:604)
	at org.eclipse.jface.viewers.AbstractTableViewer.lambda$0(AbstractTableViewer.java:566)
	at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1447)
	at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1408)
	at org.eclipse.jface.viewers.AbstractTableViewer.inputChanged(AbstractTableViewer.java:566)
	at org.eclipse.jface.viewers.ContentViewer.setInput(ContentViewer.java:286)
	at org.eclipse.jface.viewers.StructuredViewer.setInput(StructuredViewer.java:1685)
	at org.eclipse.wst.server.ui.internal.viewers.MonitorDialog.createDialogArea(MonitorDialog.java:123)
	at org.eclipse.jface.dialogs.Dialog.createContents(Dialog.java:768)
	at org.eclipse.jface.window.Window.create(Window.java:426)
	at org.eclipse.jface.dialogs.Dialog.create(Dialog.java:1096)
	at org.eclipse.jface.window.Window.open(Window.java:783)
	at org.eclipse.wst.server.ui.internal.viewers.MonitorComposite$2.widgetSelected(MonitorComposite.java:135)
	at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:249)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:86)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4428)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1079)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4238)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3817)
	at org.eclipse.jface.window.Window.runEventLoop(Window.java:818)
	at org.eclipse.jface.window.Window.open(Window.java:794)
	at org.eclipse.wst.server.ui.internal.view.servers.PropertiesAction.perform(PropertiesAction.java:49)
	at org.eclipse.wst.server.ui.internal.view.servers.AbstractServerAction.run(AbstractServerAction.java:64)
	at org.eclipse.jface.action.Action.runWithEvent(Action.java:473)
	at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:565)
	at org.eclipse.jface.action.ActionContributionItem.lambda$4(ActionContributionItem.java:397)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:86)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4428)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1079)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4238)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3817)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1150)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1039)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:153)
	at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:680)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:594)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:148)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:151)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:388)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:243)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:653)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:590)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1499)
	at org.eclipse.equinox.launcher.Main.main(Main.java:1472)