Description of problem:
An exception appears to occur randomly while working in the web admin application, in particular it seems related to the system tree

Version-Release number of selected component (if applicable):


How reproducible:
???

Steps to Reproduce:
???

Additional info:
The UI.log has the following stack trace:
2016-10-20 09:13:24,742 ERROR
    [org.ovirt.engine.ui.frontend.server.gwt.OvirtRemoteLoggingService]
    (default task-7) [] Permutation name: 430985F23DFC1C8BE1C7FDD91EDAA785
    2016-10-20 09:13:24,747 ERROR
    [org.ovirt.engine.ui.frontend.server.gwt.OvirtRemoteLoggingService]
    (default task-7) [] Uncaught exception: :
    com.google.gwt.event.shared.UmbrellaException: Exception caught:
    Exception caught: (TypeError)
      __gwt$exception: <skipped>: Cannot read property 'f' of null
         at java.lang.Throwable.fillInStackTrace(Throwable.java:114)
    [rt.jar:1.8.0_102]
         at
    java.lang.RuntimeException.RuntimeException(RuntimeException.java:32)
    [rt.jar:1.8.0_102]
         at
    com.google.web.bindery.event.shared.UmbrellaException.UmbrellaException(UmbrellaException.java:70)
    [gwt-servlet.jar:]
         at
    com.google.gwt.event.shared.UmbrellaException.UmbrellaException(UmbrellaException.java:25)
    [gwt-servlet.jar:]
         at
    com.google.gwt.event.shared.HandlerManager.$fireEvent(HandlerManager.java:117)
    [gwt-servlet.jar:]
         at
    com.google.gwt.view.client.SelectionChangeEvent.fire(SelectionChangeEvent.java:67)
    [gwt-servlet.jar:]
         at
    com.google.gwt.view.client.SingleSelectionModel.$resolveChanges(SingleSelectionModel.java:118)
    [gwt-servlet.jar:]
         at
    com.google.gwt.view.client.SingleSelectionModel.isSelected(SingleSelectionModel.java:82)
    [gwt-servlet.jar:]
         at
    com.google.gwt.user.cellview.client.HasDataPresenter.$resolvePendingState(HasDataPresenter.java:1062)
    [gwt-servlet.jar:]
         at
    com.google.gwt.user.cellview.client.CellTreeNodeView$TreeNodeImpl.$getChildCount(CellTreeNodeView.java:573)
    [gwt-servlet.jar:]
         at
    org.ovirt.engine.ui.webadmin.widget.tree.SystemTree.$expandTree(SystemTree.java:229)
         at
    org.ovirt.engine.ui.webadmin.widget.tree.SystemTree$3.eventRaised(SystemTree.java:110)
         at org.ovirt.engine.ui.uicompat.Event.$raise(Event.java:114)
         at
    org.ovirt.engine.ui.uicommonweb.models.SearchableListModel.$setItems(SearchableListModel.java:802)
         at
    org.ovirt.engine.ui.uicommonweb.models.SystemTreeModel.$executed(SystemTreeModel.java:438)
         at
    org.ovirt.engine.ui.uicommonweb.models.SystemTreeModel.executed(SystemTreeModel.java:438)
         at
    org.ovirt.engine.ui.frontend.Frontend$3.$onSuccess(Frontend.java:344)
    [frontend.jar:]
         at
    org.ovirt.engine.ui.frontend.Frontend$3.onSuccess(Frontend.java:344)
    [frontend.jar:]
         at
    org.ovirt.engine.ui.frontend.communication.OperationProcessor$3.$onSuccess(OperationProcessor.java:178)
    [frontend.jar:]
         at
    org.ovirt.engine.ui.frontend.communication.OperationProcessor$3.onSuccess(OperationProcessor.java:178)
    [frontend.jar:]
         at
    org.ovirt.engine.ui.frontend.communication.GWTRPCCommunicationProvider$5$1.$onSuccess(GWTRPCCommunicationProvider.java:271)
    [frontend.jar:]
         at
    org.ovirt.engine.ui.frontend.communication.GWTRPCCommunicationProvider$5$1.onSuccess(GWTRPCCommunicationProvider.java:271)
    [frontend.jar:]
         at
    com.google.gwt.rpc.client.impl.RpcCallbackAdapter.onResponseReceived(RpcCallbackAdapter.java:72)
    [gwt-servlet.jar:]
         at
    org.ovirt.engine.ui.common.gin.BaseSystemModule$1$1.onResponseReceived(BaseSystemModule.java:140)
         at
    com.google.gwt.http.client.Request.$fireOnResponseReceived(Request.java:237)
    [gwt-servlet.jar:]
         at
    com.google.gwt.http.client.RequestBuilder$1.onReadyStateChange(RequestBuilder.java:409)
    [gwt-servlet.jar:]
         at
    Unknown.<anonymous>(https://ovirttest.netbulae.test/ovirt-engine/webadmin/430985F23DFC1C8BE1C7FDD91EDAA785.cache.html@65)
    at com.google.gwt.core.client.impl.Impl.apply(Impl.java:296)
    [gwt-servlet.jar:]
         at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:335)
    [gwt-servlet.jar:]
         at
    Unknown.<anonymous>(https://ovirttest.netbulae.test/ovirt-engine/webadmin/430985F23DFC1C8BE1C7FDD91EDAA785.cache.html@54)Caused
    by: com.google.gwt.event.shared.UmbrellaException: Exception caught:
    (TypeError)
      __gwt$exception: <skipped>: Cannot read property 'f' of null
         at java.lang.Throwable.fillInStackTrace(Throwable.java:114)
    [rt.jar:1.8.0_102]
         at
    java.lang.RuntimeException.RuntimeException(RuntimeException.java:32)
    [rt.jar:1.8.0_102]
         at
    com.google.web.bindery.event.shared.UmbrellaException.UmbrellaException(UmbrellaException.java:70)
    [gwt-servlet.jar:]
         at
    com.google.gwt.event.shared.UmbrellaException.UmbrellaException(UmbrellaException.java:25)
    [gwt-servlet.jar:]
         at
    com.google.gwt.event.shared.EventBus.$castFireEvent(EventBus.java:65)
    [gwt-servlet.jar:]
         at
    org.ovirt.engine.ui.webadmin.uicommon.model.SystemTreeSelectionChangeEvent.fire(SystemTreeSelectionChangeEvent.java:21)
         at
    org.ovirt.engine.ui.webadmin.uicommon.model.SystemTreeModelProvider.$setSelectedItems(SystemTreeModelProvider.java:108)
         at
    org.ovirt.engine.ui.webadmin.uicommon.model.SystemTreeModelProvider$1.onSelectionChange(SystemTreeModelProvider.java:59)
         at
    com.google.gwt.view.client.SelectionChangeEvent.dispatch(SelectionChangeEvent.java:98)
    [gwt-servlet.jar:]
         at
    com.google.gwt.event.shared.GwtEvent.dispatch(GwtEvent.java:76)
    [gwt-servlet.jar:]
         at
    com.google.web.bindery.event.shared.SimpleEventBus.$doFire(SimpleEventBus.java:173)
    [gwt-servlet.jar:]
         ... 26 more
    Caused by: com.google.gwt.core.client.JavaScriptException: (TypeError)
      __gwt$exception: <skipped>: Cannot read property 'f' of null
         at
    org.ovirt.engine.ui.webadmin.plugin.entity.SystemTreeItemObject.from(SystemTreeItemObject.java:15)
         at
    org.ovirt.engine.ui.webadmin.uicommon.model.SystemTreeSelectionChangeEvent.$dispatch(SystemTreeSelectionChangeEvent.java:50)
         at
    org.ovirt.engine.ui.webadmin.uicommon.model.SystemTreeSelectionChangeEvent.dispatch(SystemTreeSelectionChangeEvent.java:50)
         at
    com.google.gwt.event.shared.GwtEvent.dispatch(GwtEvent.java:76)
    [gwt-servlet.jar:]
         at
    com.google.web.bindery.event.shared.SimpleEventBus.$doFire(SimpleEventBus.java:173)
    [gwt-servlet.jar:]
         ... 33 more