ArgumentNullException: 值不能为 null。
参数名: dp
StackTrace:
   在 System.Windows.DependencyObject.GetValueSource(DependencyProperty dp, PropertyMetadata metadata, Boolean& hasModifiers, Boolean& isExpression, Boolean& isAnimated, Boolean& isCoerced, Boolean& isCurrent)
   在 System.Windows.FrameworkElement.ShouldUseSystemFont(FrameworkElement fe, DependencyProperty dp)
   在 System.Windows.FrameworkElement.CoerceFontStyle(DependencyObject o, Object value)
   在 System.Windows.DependencyObject.ProcessCoerceValue(DependencyProperty dp, PropertyMetadata metadata, EntryIndex& entryIndex, Int32& targetIndex, EffectiveValueEntry& newEntry, EffectiveValueEntry& oldEntry, Object& oldValue, Object baseValue, Object controlValue, CoerceValueCallback coerceValueCallback, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, Boolean skipBaseValueChecks)
   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.CoerceValue(DependencyProperty dp)
   在 System.Windows.SystemResources.InvalidateTreeResources(Object args)
   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)