NullReferenceException: 未将对象引用设置到对象的实例。
StackTrace:
   在 System.Collections.Generic.List`1.GetEnumerator()
   在 System.Windows.DescendentsWalker`1.WalkFrameworkElementLogicalThenVisualChildren(FrameworkElement feParent, Boolean hasLogicalChildren)
   在 System.Windows.DescendentsWalker`1.IterateChildren(DependencyObject d)
   在 System.Windows.DescendentsWalker`1.StartWalk(DependencyObject startNode, Boolean skipStartNode)
   在 MS.Internal.PrePostDescendentsWalker`1.StartWalk(DependencyObject startNode, Boolean skipStartNode)
   在 System.Windows.TreeWalkHelper.InvalidateOnTreeChange(FrameworkElement fe, FrameworkContentElement fce, DependencyObject parent, Boolean isAddOperation)
   在 System.Windows.FrameworkElement.ChangeLogicalParent(DependencyObject newParent)
   在 System.Windows.FrameworkElement.RemoveLogicalChild(Object child)
   在 System.Windows.Controls.ContentControl.OnContentChanged(Object oldContent, Object newContent)
   在 System.Windows.Controls.ContentControl.OnContentChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
   在 System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
   在 System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
   在 System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
   在 System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
   在 System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
   在 Quicker.View.Controls.IconControl.<UpdateIconAsync>d__28.MoveNext()
--- 引发异常的上一位置中堆栈跟踪的末尾 ---
   在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   在 System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   在 System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)