Layout restore of floating window return NullReferenceException

Start at DockingManager.cs line 2160 and reproduce layout restoration with a document window derived from ContentControl. Trace the ResourceDictionary and ContentPresenter failure shown in the stack trace; done means restoring and showing the floating window without the NullReferenceException.

Hallo
I get this exception in the docking manger: I hope the document window class can be a derived ContentControl.

public partial class MyDockWindow: ContentControl {
}

System.NullReferenceException
  HResult=0x80004003
  Message=Der Objektverweis wurde nicht auf eine Objektinstanz festgelegt.
  Source=PresentationFramework
  StackTrace:
   at System.Windows.ResourceDictionary.OnGettingValue(Object key, Object& value, Boolean& canCache)
   at System.Windows.ResourceDictionary.OnGettingValuePrivate(Object key, Object& value, Boolean& canCache)
   at System.Windows.ResourceDictionary.GetValueWithoutLock(Object key, Boolean& canCache)
   at System.Windows.ResourceDictionary.GetValue(Object key, Boolean& canCache)
   at System.Windows.FrameworkElement.FindBestMatchInResourceDictionary(ResourceDictionary table, ArrayList keys, Int32 exactMatch, Int32& bestMatch)
   at System.Windows.FrameworkElement.FindTemplateResourceInTree(DependencyObject target, ArrayList keys, Int32 exactMatch, Int32& bestMatch)
   at System.Windows.FrameworkElement.FindTemplateResourceInternal(DependencyObject target, Object item, Type templateType)
   at System.Windows.Controls.ContentPresenter.DefaultSelector.SelectTemplate(Object item, DependencyObject container)
   at System.Windows.Controls.ContentPresenter.ChooseTemplate()
   at System.Windows.Controls.ContentPresenter.EnsureTemplate()
   at System.Windows.Controls.ContentPresenter.OnPreApplyTemplate()
   at System.Windows.FrameworkElement.ApplyTemplate()
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Border.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Control.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
   at System.Windows.Controls.ContentPresenter.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
   at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged)
   at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Border.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Documents.AdornerDecorator.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Window.MeasureOverrideHelper(Size constraint)
   at System.Windows.Window.MeasureOverride(Size availableSize)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Interop.HwndSource.SetLayoutSize()
   at System.Windows.Interop.HwndSource.set_RootVisualInternal(Visual value)
   at System.Windows.Window.SetRootVisual()
   at System.Windows.Window.SetRootVisualAndUpdateSTC()
   at System.Windows.Window.SetupInitialState(Double requestedTop, Double requestedLeft, Double requestedWidth, Double requestedHeight)
   at System.Windows.Window.CreateSourceWindow(Boolean duringShow)
   at System.Windows.Window.ShowHelper(Object booleanBox)
   at Xceed.Wpf.AvalonDock.DockingManager.CreateUIElementForModel(ILayoutElement model) in C:\Users\c565698\Documents\Git\radax\Xceed.Wpf.AvalonDock\DockingManager.cs:line 2160