Remove Contract usages.

src/Markup/Avalonia.Markup/Data/Binding.cs

@@ -63,7 +63,8 @@ namespace Avalonia.Data
 
         protected override ExpressionObserver CreateExpressionObserver(IAvaloniaObject target, AvaloniaProperty targetProperty, object? anchor, bool enableDataValidation)
         {
-            Contract.Requires<ArgumentNullException>(target is not null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));
+
             anchor = anchor ?? DefaultAnchor?.Target;
             
             enableDataValidation = enableDataValidation && Priority == BindingPriority.LocalValue;

src/Markup/Avalonia.Markup/Data/BindingBase.cs

@@ -87,7 +87,8 @@ namespace Avalonia.Data
             object? anchor = null,
             bool enableDataValidation = false)
         {
-            Contract.Requires<ArgumentNullException>(target != null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));
+
             anchor = anchor ?? DefaultAnchor?.Target;
 
             enableDataValidation = enableDataValidation && Priority == BindingPriority.LocalValue;
@@ -135,7 +136,7 @@ namespace Avalonia.Data
             bool targetIsDataContext,
             object? anchor)
         {
-            Contract.Requires<ArgumentNullException>(target != null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));
 
             if (!(target is IDataContextProvider))
             {
@@ -166,7 +167,7 @@ namespace Avalonia.Data
             string elementName,
             ExpressionNode node)
         {
-            Contract.Requires<ArgumentNullException>(target != null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));
 
             if (NameScope is null || !NameScope.TryGetTarget(out var scope) || scope is null)
                 throw new InvalidOperationException("Name scope is null or was already collected");
@@ -182,7 +183,7 @@ namespace Avalonia.Data
             RelativeSource relativeSource,
             ExpressionNode node)
         {
-            Contract.Requires<ArgumentNullException>(target != null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));
 
             IObservable<object?> controlLocator;
 
@@ -214,7 +215,7 @@ namespace Avalonia.Data
             object source,
             ExpressionNode node)
         {
-            Contract.Requires<ArgumentNullException>(source != null);
+            _ = source ?? throw new ArgumentNullException(nameof(source));
 
             return new ExpressionObserver(source, node);
         }
@@ -223,7 +224,7 @@ namespace Avalonia.Data
             IAvaloniaObject target,
             ExpressionNode node)
         {
-            Contract.Requires<ArgumentNullException>(target is not null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));
 
             var result = new ExpressionObserver(
                 () => target.GetValue(StyledElement.TemplatedParentProperty),

src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionObserverBuilder.cs

@@ -48,7 +48,8 @@ namespace Avalonia.Markup.Parsers
             string? description = null,
             Func<string, string, Type>? typeResolver = null)
         {
-            Contract.Requires<ArgumentNullException>(rootObservable != null);
+            _ = rootObservable ?? throw new ArgumentNullException(nameof(rootObservable));
+
             return new ExpressionObserver(
                 rootObservable,
                 Parse(expression, enableDataValidation, typeResolver).Node,
@@ -64,7 +65,7 @@ namespace Avalonia.Markup.Parsers
             string? description = null,
             Func<string, string, Type>? typeResolver = null)
         {
-            Contract.Requires<ArgumentNullException>(rootGetter != null);
+            _ = rootGetter ?? throw new ArgumentNullException(nameof(rootGetter));
 
             return new ExpressionObserver(
                 rootGetter,