diff --git a/Ghis.Controls/Charts/ChartLines.cs b/Ghis.Controls/Charts/ChartLines.cs
index d097a32..47b85e5 100644
--- a/Ghis.Controls/Charts/ChartLines.cs
+++ b/Ghis.Controls/Charts/ChartLines.cs
@@ -50,8 +50,7 @@ protected override void OnRender(DrawingContext drawingContext)
 
         public static void OnVerticalAxisTickValuesChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
         {
-            ChartLines obj = sender as ChartLines;
-            if (obj != null && obj.VerticalAxisTickPositions != null)
+            if (sender is ChartLines obj && obj.VerticalAxisTickPositions != null)
             {
                 obj.InvalidateVisual();
                 obj.VerticalAxisTickPositions.CollectionChanged += new NotifyCollectionChangedEventHandler(obj.VerticalAxisTickPositions_CollectionChanged);
diff --git a/Ghis.Controls/Charts/ValueExtractor.cs b/Ghis.Controls/Charts/ValueExtractor.cs
index c3fd8e8..0c66966 100644
--- a/Ghis.Controls/Charts/ValueExtractor.cs
+++ b/Ghis.Controls/Charts/ValueExtractor.cs
@@ -37,15 +37,15 @@ private static void OnItemsChanged(DependencyObject sender, DependencyPropertyCh
             }
             // ValueExtractor v = sender as ValueExtractor;
             // ItemCollection oldItems = args.OldValue as ItemCollection;
-            ItemCollection newItems = args.NewValue as ItemCollection;
+            ItemCollection? newItems = args.NewValue as ItemCollection;
             if (args.OldValue is INotifyCollectionChanged oldItems)
             {
-                oldItems.CollectionChanged -= new NotifyCollectionChangedEventHandler(v.OnItemsCollectionChanged);
+                oldItems.CollectionChanged -= new NotifyCollectionChangedEventHandler(v.OnItemsCollectionChanged!);
             }
 
             if (v.Items is INotifyCollectionChanged vItems)
             {
-                vItems.CollectionChanged += new NotifyCollectionChangedEventHandler(v.OnItemsCollectionChanged);
+                vItems.CollectionChanged += new NotifyCollectionChangedEventHandler(v.OnItemsCollectionChanged!);
                 if (v.ValuePath is not null)
                 {
                     v.GenerateValueList();