diff --git a/Elwig/Windows/ChartWindow.xaml.cs b/Elwig/Windows/ChartWindow.xaml.cs
index b470523..9bd7601 100644
--- a/Elwig/Windows/ChartWindow.xaml.cs
+++ b/Elwig/Windows/ChartWindow.xaml.cs
@@ -26,12 +26,12 @@ namespace Elwig.Windows {
         private bool HasChanged = false;
         private bool Updating = false;
 
-        private Scatter DataPlot;
+        private Scatter? DataPlot;
         private Scatter? GebundenPlot;
-        private Marker HighlightedPointPlot;
-        private Marker PrimaryMarkedPointPlot;
-        private Marker SecondaryMarkedPointPlot;
-        private Text TooltipPlot;
+        private Marker? HighlightedPointPlot;
+        private Marker? PrimaryMarkedPointPlot;
+        private Marker? SecondaryMarkedPointPlot;
+        private Text? TooltipPlot;
 
         private static readonly LegendItem
             UngebundenLegend = new() {
@@ -77,7 +77,7 @@ namespace Elwig.Windows {
             PriceInput.Unit = $"{CurrencySymbol}/kg";
             GebundenFlatBonus.Unit = $"{CurrencySymbol}/kg";
             PaymentVar = ctx.PaymentVariants.Find(year, avnr) ?? throw new ArgumentException("PaymentVar not found");
-            Title = $"{PaymentVar?.Name} - Lese {year} - Elwig";
+            Title = $"{PaymentVar.Name} - Lese {year} - Elwig";
             LockContext = true;
         }
 
@@ -215,10 +215,12 @@ namespace Elwig.Windows {
                 GebundenPlot.MarkerStyle = new MarkerStyle(MarkerShape.FilledCircle, 9, ColorGebunden);
             }
 
-            DataPlot = OechslePricePlot.Plot.Add.Scatter(SelectedGraphEntry!.DataGraph.DataX, SelectedGraphEntry!.DataGraph.DataY);
-            DataPlot.LineStyle.Color = ColorUngebunden;
-            DataPlot.Color = ColorUngebunden;
-            DataPlot.MarkerStyle = new MarkerStyle(MarkerShape.FilledCircle, 9, ColorUngebunden);
+            if (SelectedGraphEntry != null) {
+                DataPlot = OechslePricePlot.Plot.Add.Scatter(SelectedGraphEntry.DataGraph.DataX, SelectedGraphEntry.DataGraph.DataY);
+                DataPlot.LineStyle.Color = ColorUngebunden;
+                DataPlot.Color = ColorUngebunden;
+                DataPlot.MarkerStyle = new MarkerStyle(MarkerShape.FilledCircle, 9, ColorUngebunden);
+            }
 
             OechslePricePlot.Plot.Axes.SetLimits(Math.Min(GraphEntry.MinX, GraphEntry.MinXGeb) - 1, GraphEntry.MaxX + 1, -0.1, 1.5);
 
@@ -244,7 +246,10 @@ namespace Elwig.Windows {
             SecondaryMarkedPoint = -1;
             ChangeActiveGraph(null);
             HideGradationLines();
-            OechslePricePlot.Plot.Remove(DataPlot);
+            if (DataPlot != null) {
+                OechslePricePlot.Plot.Remove(DataPlot);
+                DataPlot = null;
+            }
             if (GebundenPlot != null) {
                 OechslePricePlot.Plot.Remove(GebundenPlot);
                 GebundenPlot = null;
@@ -254,9 +259,9 @@ namespace Elwig.Windows {
             OechslePricePlot.Refresh();
         }
 
-        private void ChangeMarker(Marker point, bool visible, double x = 0, double y = 0) {
-            point.Location = new Coordinates(x, y);
-            point.IsVisible = visible;
+        private static void ChangeMarker(Marker? point, bool visible, double x = 0, double y = 0) {
+            point?.Location = new Coordinates(x, y);
+            point?.IsVisible = visible;
         }
 
         private void EnableActionButtons() {
@@ -416,7 +421,7 @@ namespace Elwig.Windows {
                 var res = Validator.CheckDecimal(PriceInput, true, 2, Season.Precision);
                 if (res.IsValid && double.TryParse(PriceInput.Text, out double price)) {
                     ActiveGraph.SetPriceAt(PrimaryMarkedPoint, price);
-                    PrimaryMarkedPointPlot.Location = new Coordinates(PrimaryMarkedPointPlot.Location.X, price);
+                    PrimaryMarkedPointPlot?.Location = new Coordinates(PrimaryMarkedPointPlot.Location.X, price);
                     SetHasChanged();
                     OechslePricePlot.Refresh();
                     CheckGebundenTypeFixed();
@@ -492,17 +497,19 @@ namespace Elwig.Windows {
 
                 ChangeMarker(PrimaryMarkedPointPlot, true, ActiveGraph.GetOechsleAt(PrimaryMarkedPoint), ActiveGraph.GetPriceAt(PrimaryMarkedPoint));
 
-                Updating = true;
-                OechsleInput.Text = Highlighted.Graph!.GetOechsleAt(Highlighted.Index).ToString();
-                GebInput.IsChecked = Highlighted.Graph == SelectedGraphEntry?.GebundenGraph;
-                PriceInput.Text = Math.Round(Highlighted.Graph.GetPriceAt(Highlighted.Index), Season.Precision).ToString();
-                Updating = false;
+                if (Highlighted.Graph != null) {
+                    Updating = true;
+                    OechsleInput.Text = Highlighted.Graph.GetOechsleAt(Highlighted.Index).ToString();
+                    GebInput.IsChecked = Highlighted.Graph == SelectedGraphEntry?.GebundenGraph;
+                    PriceInput.Text = Math.Round(Highlighted.Graph.GetPriceAt(Highlighted.Index), Season.Precision).ToString();
+                    Updating = false;
+                }
 
                 EnableActionButtons();
             } else {
                 PrimaryMarkedPoint = -1;
                 SecondaryMarkedPoint = -1;
-                if (SelectedGraphEntry!.GebundenGraph != null) {
+                if (SelectedGraphEntry?.GebundenGraph != null) {
                     ChangeActiveGraph(null);
                 }
                 ChangeMarker(PrimaryMarkedPointPlot, false);
@@ -548,21 +555,26 @@ namespace Elwig.Windows {
 
             if (mouseOnData != null) {
                 ChangeMarker(HighlightedPointPlot, true, mouseOnData.Value.X, mouseOnData.Value.Y);
-                HighlightedPointPlot.IsVisible = true;
+                HighlightedPointPlot?.IsVisible = true;
                 HoverChanged = true ^ HoverActive;
                 HoverActive = true;
-                HandleTooltip(mouseOnData.Value.X, mouseOnData.Value.Y, mouseOnData.Value.Index, SelectedGraphEntry!.DataGraph, e.GetPosition(OechslePricePlot), e is MouseWheelEventArgs);
+                if (SelectedGraphEntry?.DataGraph is Graph g)
+                    HandleTooltip(mouseOnData.Value.X, mouseOnData.Value.Y, mouseOnData.Value.Index, g, e.GetPosition(OechslePricePlot), e is MouseWheelEventArgs);
             } else if (mouseOnGebunden != null) {
                 ChangeMarker(HighlightedPointPlot, true, mouseOnGebunden.Value.X, mouseOnGebunden.Value.Y);
-                HighlightedPointPlot.IsVisible = true;
+                HighlightedPointPlot?.IsVisible = true;
                 HoverChanged = true ^ HoverActive;
                 HoverActive = true;
-                HandleTooltip(mouseOnGebunden.Value.X, mouseOnGebunden.Value.Y, mouseOnGebunden.Value.Index, SelectedGraphEntry!.GebundenGraph!, e.GetPosition(OechslePricePlot), e is MouseWheelEventArgs);
+                if (SelectedGraphEntry?.GebundenGraph is Graph g)
+                    HandleTooltip(mouseOnGebunden.Value.X, mouseOnGebunden.Value.Y, mouseOnGebunden.Value.Index, g, e.GetPosition(OechslePricePlot), e is MouseWheelEventArgs);
             } else {
                 ChangeMarker(HighlightedPointPlot, false);
                 HoverChanged = false ^ HoverActive;
                 HoverActive = false;
-                OechslePricePlot.Plot.PlottableList.Remove(TooltipPlot);
+                if (TooltipPlot != null) {
+                    OechslePricePlot.Plot.PlottableList.Remove(TooltipPlot);
+                    TooltipPlot = null;
+                }
                 OechslePricePlot.Refresh();
             }
         }
@@ -577,7 +589,10 @@ namespace Elwig.Windows {
 
         private void HandleTooltip(double pointX, double pointY, int pointIndex, Graph g, Point p, bool force) {
             if (force || LastHighlighted != Highlighted || HoverChanged) {
-                OechslePricePlot.Plot.PlottableList.Remove(TooltipPlot);
+                if (TooltipPlot != null) {
+                    OechslePricePlot.Plot.PlottableList.Remove(TooltipPlot);
+                    TooltipPlot = null;
+                }
                 if (TooltipInput.IsChecked == true) {
                     Coordinates mouseLocation = GetMouseCoordinates(new(p.X, p.Y - 30));
                     TooltipPlot = OechslePricePlot.Plot.Add.Text($"Oechsle: {pointX:N2}, Preis: {Math.Round(pointY, Season.Precision)} {CurrencySymbol}/kg", mouseLocation.X, mouseLocation.Y);
@@ -676,7 +691,7 @@ namespace Elwig.Windows {
             }
         }
 
-        private void DisableTextBox(TextBox u) {
+        private static void DisableTextBox(TextBox u) {
             u.IsEnabled = false;
             u.IsReadOnly = true;
         }
@@ -707,10 +722,8 @@ namespace Elwig.Windows {
             ActiveGraph = g;
         }
 
-        private void ChangeLineWidth(Scatter? p, double lineWidth) {
-            if (p != null) {
-                p.LineWidth = (float)lineWidth;
-            }
+        private static void ChangeLineWidth(Scatter? p, double lineWidth) {
+            p?.LineWidth = (float)lineWidth;
         }
 
         private void GraphList_SelectionChanged(object sender, SelectionChangedEventArgs e) {
@@ -752,7 +765,7 @@ namespace Elwig.Windows {
                 }
             }
 
-            SelectedGraphEntry!.Vaributes = VaributeInput.SelectedItems.Cast<Varibute>().ToList();
+            SelectedGraphEntry?.Vaributes = [.. VaributeInput.SelectedItems.Cast<Varibute>()];
             SetHasChanged();
             GraphList.Items.Refresh();
             VaributeInput.Items.Refresh();