Finished adding nullable annotations to Avalonia.Base.

4 years ago · 76667dbd0d
182 changed files with 420 additions and 599 deletions
--- a/src/Avalonia.Base/AttachedProperty.cs
+++ b/src/Avalonia.Base/AttachedProperty.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/Avalonia.Base.csproj
+++ b/src/Avalonia.Base/Avalonia.Base.csproj
@ -11,4 +11,5 @@
  <Import Project="..\..\build\JetBrains.Annotations.props" />
  <Import Project="..\..\build\System.Memory.props" />
  <Import Project="..\..\build\ApiDiff.props" />
+  <Import Project="..\..\build\NullableEnable.props" />
 </Project>
--- a/src/Avalonia.Base/AvaloniaInternalException.cs
+++ b/src/Avalonia.Base/AvaloniaInternalException.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/AvaloniaLocator.cs
+++ b/src/Avalonia.Base/AvaloniaLocator.cs
@ -7,10 +7,10 @@ namespace Avalonia
 {
    public class AvaloniaLocator : IAvaloniaDependencyResolver
    {
-        private readonly IAvaloniaDependencyResolver _parentScope;
+        private readonly IAvaloniaDependencyResolver? _parentScope;
        public static IAvaloniaDependencyResolver Current { get; set; }
        public static AvaloniaLocator CurrentMutable { get; set; }
-        private readonly Dictionary<Type, Func<object>> _registry = new Dictionary<Type, Func<object>>();
+        private readonly Dictionary<Type, Func<object?>> _registry = new Dictionary<Type, Func<object?>>();

        static AvaloniaLocator()
        {
@ -27,10 +27,9 @@ namespace Avalonia
            _parentScope = parentScope;
        }

-        public object GetService(Type t)
+        public object? GetService(Type t)
        {
-            Func<object> rv;
-            return _registry.TryGetValue(t, out rv) ? rv() : _parentScope?.GetService(t);
+            return _registry.TryGetValue(t, out var rv) ? rv() : _parentScope?.GetService(t);
        }

        public class RegistrationHelper<TService>
@ -57,7 +56,7 @@ namespace Avalonia
            public AvaloniaLocator ToLazy<TImlp>(Func<TImlp> func) where TImlp : TService
            {
                var constructed = false;
-                TImlp instance = default;
+                TImlp? instance = default;
                _locator._registry[typeof (TService)] = () =>
                {
                    if (!constructed)
@ -73,7 +72,7 @@ namespace Avalonia
            
            public AvaloniaLocator ToSingleton<TImpl>() where TImpl : class, TService, new()
            {
-                TImpl instance = null;
+                TImpl? instance = null;
                return ToFunc(() => instance ?? (instance = new TImpl()));
            }

@ -117,14 +116,14 @@ namespace Avalonia

    public interface IAvaloniaDependencyResolver
    {
-        object GetService(Type t);
+        object? GetService(Type t);
    }

    public static class LocatorExtensions
    {
-        public static T GetService<T>(this IAvaloniaDependencyResolver resolver)
+        public static T? GetService<T>(this IAvaloniaDependencyResolver resolver)
        {
-            return (T) resolver.GetService(typeof (T));
+            return (T?) resolver.GetService(typeof (T));
        }
    }
 }
--- a/src/Avalonia.Base/AvaloniaObject.cs
+++ b/src/Avalonia.Base/AvaloniaObject.cs
@ -7,8 +7,6 @@ using Avalonia.Logging;
 using Avalonia.PropertyStore;
 using Avalonia.Threading;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
@ -47,7 +45,7 @@ namespace Avalonia
        /// <summary>
        /// Raised when a <see cref="AvaloniaProperty"/> value changes on this object.
        /// </summary>
-        event PropertyChangedEventHandler INotifyPropertyChanged.PropertyChanged
+        event PropertyChangedEventHandler? INotifyPropertyChanged.PropertyChanged
        {
            add { _inpcChanged += value; }
            remove { _inpcChanged -= value; }
@ -857,7 +855,7 @@ namespace Avalonia
        private string GetDescription(object o)
        {
            var description = o as IDescription;
-            return description?.Description ?? o.ToString();
+            return description?.Description ?? o.ToString() ?? o.GetType().Name;
        }

        /// <summary>
--- a/src/Avalonia.Base/AvaloniaObjectExtensions.cs
+++ b/src/Avalonia.Base/AvaloniaObjectExtensions.cs
@ -6,8 +6,6 @@ using System.Reactive.Subjects;
 using Avalonia.Data;
 using Avalonia.Reactive;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/AvaloniaProperty.cs
+++ b/src/Avalonia.Base/AvaloniaProperty.cs
@ -4,8 +4,6 @@ using Avalonia.Data;
 using Avalonia.Data.Core;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
@ -544,12 +542,12 @@ namespace Avalonia
                throw new ArgumentNullException(nameof(type));
            }

-            if (_metadataCache.TryGetValue(type, out AvaloniaPropertyMetadata result))
+            if (_metadataCache.TryGetValue(type, out var result))
            {
                return result;
            }

-            Type currentType = type;
+            Type? currentType = type;

            while (currentType != null)
            {
--- a/src/Avalonia.Base/AvaloniaPropertyChangedEventArgs.cs
+++ b/src/Avalonia.Base/AvaloniaPropertyChangedEventArgs.cs
@ -1,8 +1,6 @@
 using System;
 using Avalonia.Data;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/AvaloniaPropertyChangedEventArgs`1.cs
+++ b/src/Avalonia.Base/AvaloniaPropertyChangedEventArgs`1.cs
@ -1,7 +1,5 @@
 using Avalonia.Data;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/AvaloniaPropertyMetadata.cs
+++ b/src/Avalonia.Base/AvaloniaPropertyMetadata.cs
@ -1,7 +1,5 @@
 using Avalonia.Data;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/AvaloniaPropertyRegistry.cs
+++ b/src/Avalonia.Base/AvaloniaPropertyRegistry.cs
@ -2,8 +2,6 @@ using System;
 using System.Collections.Generic;
 using System.Runtime.CompilerServices;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/AvaloniaProperty`1.cs
+++ b/src/Avalonia.Base/AvaloniaProperty`1.cs
@ -3,8 +3,6 @@ using System.Reactive.Subjects;
 using Avalonia.Data;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
@ -84,15 +82,15 @@ namespace Avalonia

        protected override IObservable<AvaloniaPropertyChangedEventArgs> GetChanged() => Changed;

-        protected BindingValue<object> TryConvert(object? value)
+        protected BindingValue<object?> TryConvert(object? value)
        {
            if (value == UnsetValue)
            {
-                return BindingValue<object>.Unset;
+                return BindingValue<object?>.Unset;
            }
            else if (value == BindingOperations.DoNothing)
            {
-                return BindingValue<object>.DoNothing;
+                return BindingValue<object?>.DoNothing;
            }

            if (!TypeUtilities.TryConvertImplicit(PropertyType, value, out var converted))
@ -102,7 +100,7 @@ namespace Avalonia
                    Name,
                    value,
                    value?.GetType().FullName ?? "(null)"));
-                return BindingValue<object>.BindingError(error);
+                return BindingValue<object?>.BindingError(error);
            }

            return converted;
--- a/src/Avalonia.Base/Collections/AvaloniaDictionary.cs
+++ b/src/Avalonia.Base/Collections/AvaloniaDictionary.cs
@ -3,11 +3,10 @@ using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Avalonia.Data.Core;

-#nullable enable
-
 namespace Avalonia.Collections
 {
    /// <summary>
@ -19,6 +18,7 @@ namespace Avalonia.Collections
        IDictionary,
        INotifyCollectionChanged,
        INotifyPropertyChanged
+            where TKey : notnull
    {
        private Dictionary<TKey, TValue> _inner;

@ -76,8 +76,7 @@ namespace Avalonia.Collections

            set
            {
-                TValue old;
-                bool replace = _inner.TryGetValue(key, out old);
+                bool replace = _inner.TryGetValue(key, out var old);
                _inner[key] = value;

                if (replace)
@ -89,7 +88,7 @@ namespace Avalonia.Collections
                        var e = new NotifyCollectionChangedEventArgs(
                            NotifyCollectionChangedAction.Replace,
                            new KeyValuePair<TKey, TValue>(key, value),
-                            new KeyValuePair<TKey, TValue>(key, old));
+                            new KeyValuePair<TKey, TValue>(key, old!));
                        CollectionChanged(this, e);
                    }
                }
@ -100,7 +99,7 @@ namespace Avalonia.Collections
            }
        }

-        object IDictionary.this[object key] { get => ((IDictionary)_inner)[key]; set => ((IDictionary)_inner)[key] = value; }
+        object? IDictionary.this[object key] { get => ((IDictionary)_inner)[key]; set => ((IDictionary)_inner)[key] = value; }

        /// <inheritdoc/>
        public void Add(TKey key, TValue value)
@ -145,7 +144,7 @@ namespace Avalonia.Collections
        /// <inheritdoc/>
        public bool Remove(TKey key)
        {
-            if (_inner.TryGetValue(key, out TValue value))
+            if (_inner.TryGetValue(key, out var value))
            {
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Count)));
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs($"Item[{key}]"));
@ -168,8 +167,7 @@ namespace Avalonia.Collections
        }

        /// <inheritdoc/>
-        public bool TryGetValue(TKey key, out TValue value) => _inner.TryGetValue(key, out value);
-
+        public bool TryGetValue(TKey key, [MaybeNullWhen(false)] out TValue value) => _inner.TryGetValue(key, out value);
        /// <inheritdoc/>
        IEnumerator IEnumerable.GetEnumerator() => _inner.GetEnumerator();

@ -195,7 +193,7 @@ namespace Avalonia.Collections
        }

        /// <inheritdoc/>
-        void IDictionary.Add(object key, object value) => Add((TKey)key, (TValue)value);
+        void IDictionary.Add(object key, object? value) => Add((TKey)key, (TValue)value!);

        /// <inheritdoc/>
        bool IDictionary.Contains(object key) => ((IDictionary) _inner).Contains(key);
--- a/src/Avalonia.Base/Collections/AvaloniaList.cs
+++ b/src/Avalonia.Base/Collections/AvaloniaList.cs
@ -6,8 +6,6 @@ using System.ComponentModel;
 using System.Linq;
 using Avalonia.Diagnostics;

-#nullable enable
-
 namespace Avalonia.Collections
 {
    /// <summary>
@ -95,7 +93,7 @@ namespace Avalonia.Collections
        /// <summary>
        /// Raised when a change is made to the collection's items.
        /// </summary>
-        public event NotifyCollectionChangedEventHandler CollectionChanged
+        public event NotifyCollectionChangedEventHandler? CollectionChanged
        {
            add => _collectionChanged += value;
            remove => _collectionChanged -= value;
@ -135,7 +133,7 @@ namespace Avalonia.Collections
        bool ICollection.IsSynchronized => false;

        /// <inheritdoc/>
-        object? ICollection.SyncRoot => null;
+        object ICollection.SyncRoot => this;

        /// <inheritdoc/>
        bool ICollection<T>.IsReadOnly => false;
--- a/src/Avalonia.Base/Collections/AvaloniaListConverter.cs
+++ b/src/Avalonia.Base/Collections/AvaloniaListConverter.cs
@ -3,8 +3,6 @@ using System.ComponentModel;
 using System.Globalization;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia.Collections
 {
    /// <summary>
@ -12,23 +10,26 @@ namespace Avalonia.Collections
    /// </summary>
    public class AvaloniaListConverter<T> : TypeConverter
    {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
        {
            return sourceType == typeof(string);
        }

-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
        {
+            if (value is not string stringValue)
+                return null;
+
            var result = new AvaloniaList<T>();

            // TODO: Use StringTokenizer here.
-            var values = ((string)value).Split(',');
+            var values = stringValue.Split(',');

            foreach (var s in values)
            {
                if (TypeUtilities.TryConvert(typeof(T), s, culture, out var v))
                {
-                    result.Add((T)v);
+                    result.Add((T)v!);
                }
                else
                {
--- a/src/Avalonia.Base/Collections/AvaloniaListExtensions.cs
+++ b/src/Avalonia.Base/Collections/AvaloniaListExtensions.cs
@ -5,8 +5,6 @@ using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Reactive.Disposables;

-#nullable enable
-
 namespace Avalonia.Collections
 {
    /// <summary>
@ -88,7 +86,7 @@ namespace Avalonia.Collections
            {
                for (var i = items.Count - 1; i >= 0; --i)
                {
-                    removed(index + i, (T)items[i]);
+                    removed(index + i, (T)items[i]!);
                }
            }

@ -97,22 +95,22 @@ namespace Avalonia.Collections
                switch (e.Action)
                {
                    case NotifyCollectionChangedAction.Add:
-                        Add(e.NewStartingIndex, e.NewItems);
+                        Add(e.NewStartingIndex, e.NewItems!);
                        break;

                    case NotifyCollectionChangedAction.Move:
                    case NotifyCollectionChangedAction.Replace:
-                        Remove(e.OldStartingIndex, e.OldItems);
+                        Remove(e.OldStartingIndex, e.OldItems!);
                        int newIndex = e.NewStartingIndex;
                        if(newIndex > e.OldStartingIndex)
                        {
-                            newIndex -= e.OldItems.Count;
+                            newIndex -= e.OldItems!.Count;
                        }
-                        Add(newIndex, e.NewItems);
+                        Add(newIndex, e.NewItems!);
                        break;

                    case NotifyCollectionChangedAction.Remove:
-                        Remove(e.OldStartingIndex, e.OldItems);
+                        Remove(e.OldStartingIndex, e.OldItems!);
                        break;

                    case NotifyCollectionChangedAction.Reset:
@ -166,7 +164,7 @@ namespace Avalonia.Collections
        /// <returns>A disposable used to terminate the subscription.</returns>
        public static IDisposable TrackItemPropertyChanged<T>(
            this IAvaloniaReadOnlyList<T> collection,
-            Action<Tuple<object, PropertyChangedEventArgs>> callback)
+            Action<Tuple<object?, PropertyChangedEventArgs>> callback)
        {
            List<INotifyPropertyChanged> tracked = new List<INotifyPropertyChanged>();

--- a/src/Avalonia.Base/Collections/IAvaloniaList.cs
+++ b/src/Avalonia.Base/Collections/IAvaloniaList.cs
@ -1,7 +1,5 @@
 using System.Collections.Generic;

-#nullable enable
-
 namespace Avalonia.Collections
 {
    /// <summary>
--- a/src/Avalonia.Base/Collections/IAvaloniaReadOnlyList.cs
+++ b/src/Avalonia.Base/Collections/IAvaloniaReadOnlyList.cs
@ -2,8 +2,6 @@ using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.ComponentModel;

-#nullable enable
-
 namespace Avalonia.Collections
 {
    /// <summary>
--- a/src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs
+++ b/src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs
@ -4,8 +4,6 @@ using System.Reactive.Linq;
 using Avalonia.Reactive;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia.Collections
 {
    public static class NotifyCollectionChangedExtensions
@ -70,14 +68,14 @@ namespace Avalonia.Collections
                _sourceReference = source;
            }

-            public void OnEvent(object sender, NotifyCollectionChangedEventArgs e)
+            public void OnEvent(object? sender, NotifyCollectionChangedEventArgs e)
            {
                PublishNext(e);
            }

            protected override void Initialize()
            {
-                if (_sourceReference.TryGetTarget(out INotifyCollectionChanged instance))
+                if (_sourceReference.TryGetTarget(out var instance))
                {
                    WeakSubscriptionManager.Subscribe(
                    instance,
@ -88,7 +86,7 @@ namespace Avalonia.Collections

            protected override void Deinitialize()
            {
-                if (_sourceReference.TryGetTarget(out INotifyCollectionChanged instance))
+                if (_sourceReference.TryGetTarget(out var instance))
                {
                    WeakSubscriptionManager.Unsubscribe(
                        instance,
--- a/src/Avalonia.Base/Collections/Pooled/ClearMode.cs
+++ b/src/Avalonia.Base/Collections/Pooled/ClearMode.cs
@ -1,8 +1,6 @@
 // This source file is adapted from the Collections.Pooled.
 // (https://github.com/jtmueller/Collections.Pooled/tree/master/Collections.Pooled/)

-#nullable enable
-
 namespace Avalonia.Collections.Pooled
 {
    /// <summary>
--- a/src/Avalonia.Base/Collections/Pooled/ICollectionDebugView.cs
+++ b/src/Avalonia.Base/Collections/Pooled/ICollectionDebugView.cs
@ -6,8 +6,6 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;

-#nullable enable
-
 namespace Avalonia.Collections.Pooled
 {
    internal sealed class ICollectionDebugView<T>
--- a/src/Avalonia.Base/Collections/Pooled/IReadOnlyPooledList.cs
+++ b/src/Avalonia.Base/Collections/Pooled/IReadOnlyPooledList.cs
@ -4,8 +4,6 @@
 using System;
 using System.Collections.Generic;

-#nullable enable
-
 namespace Avalonia.Collections.Pooled
 {
    /// <summary>
--- a/src/Avalonia.Base/Collections/Pooled/PooledList.cs
+++ b/src/Avalonia.Base/Collections/Pooled/PooledList.cs
@ -13,8 +13,6 @@ using System.Runtime.CompilerServices;
 using System.Runtime.Serialization;
 using System.Threading;

-#nullable enable
-
 namespace Avalonia.Collections.Pooled
 {
    /// <summary>
@ -656,14 +654,15 @@ namespace Avalonia.Collections.Pooled
        // compatible array type.  
        void ICollection.CopyTo(Array array, int arrayIndex)
        {
-            if ((array != null) && (array.Rank != 1))
+            _ = array ?? throw new ArgumentNullException(nameof(array));
+
+            if (array.Rank != 1)
            {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_RankMultiDimNotSupported);
            }

            try
            {
-                // Array.Copy will check for NULL.
                Array.Copy(_items, 0, array, arrayIndex, _size);
            }
            catch (ArrayTypeMismatchException)
@ -1336,7 +1335,7 @@ namespace Avalonia.Collections.Pooled
            _version++;
        }

-        public void Sort(Func<T, T, int> comparison)
+        public void Sort(Func<T?, T?, int> comparison)
        {
            if (comparison == null)
            {
@ -1442,7 +1441,7 @@ namespace Avalonia.Collections.Pooled
            _version++;
        }

-        void IDeserializationCallback.OnDeserialization(object sender)
+        void IDeserializationCallback.OnDeserialization(object? sender)
        {
            // We can't serialize array pools, so deserialized PooledLists will
            // have to use the shared pool, even if they were using a custom pool
@ -1522,14 +1521,14 @@ namespace Avalonia.Collections.Pooled

        private readonly struct Comparer : IComparer<T>
        {
-            private readonly Func<T, T, int> _comparison;
+            private readonly Func<T?, T?, int> _comparison;

-            public Comparer(Func<T, T, int> comparison)
+            public Comparer(Func<T?, T?, int> comparison)
            {
                _comparison = comparison;
            }

-            public int Compare(T x, T y) => _comparison(x, y);
+            public int Compare(T? x, T? y) => _comparison(x, y);
        }
    }
 }
--- a/src/Avalonia.Base/Collections/Pooled/PooledStack.cs
+++ b/src/Avalonia.Base/Collections/Pooled/PooledStack.cs
@ -20,8 +20,6 @@ using System.Runtime.CompilerServices;
 using System.Runtime.Serialization;
 using System.Threading;

-#nullable enable
-
 namespace Avalonia.Collections.Pooled
 {
    /// <summary>
@ -613,7 +611,7 @@ namespace Avalonia.Collections.Pooled
            _version++;
        }

-        void IDeserializationCallback.OnDeserialization(object sender)
+        void IDeserializationCallback.OnDeserialization(object? sender)
        {
            // We can't serialize array pools, so deserialized PooledStacks will
            // have to use the shared pool, even if they were using a custom pool
--- a/src/Avalonia.Base/Collections/Pooled/StackDebugView.cs
+++ b/src/Avalonia.Base/Collections/Pooled/StackDebugView.cs
@ -5,8 +5,6 @@
 using System;
 using System.Diagnostics;

-#nullable enable
-
 namespace Avalonia.Collections.Pooled
 {
    internal sealed class StackDebugView<T>
--- a/src/Avalonia.Base/Collections/Pooled/ThrowHelper.cs
+++ b/src/Avalonia.Base/Collections/Pooled/ThrowHelper.cs
@ -42,8 +42,6 @@ using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Runtime.Serialization;

-#nullable enable
-
 namespace Avalonia.Collections.Pooled
 {
    internal static class ThrowHelper
--- a/src/Avalonia.Base/Data/AssignBindingAttribute.cs
+++ b/src/Avalonia.Base/Data/AssignBindingAttribute.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/BindingChainException.cs
+++ b/src/Avalonia.Base/Data/BindingChainException.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/BindingMode.cs
+++ b/src/Avalonia.Base/Data/BindingMode.cs
@ -1,5 +1,3 @@
-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/BindingNotification.cs
+++ b/src/Avalonia.Base/Data/BindingNotification.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
@ -214,8 +212,10 @@ namespace Avalonia.Data
        /// <param name="type">The error type.</param>
        public void AddError(Exception e, BindingErrorType type)
        {
-            Contract.Requires<ArgumentNullException>(e != null);
-            Contract.Requires<ArgumentException>(type != BindingErrorType.None);
+            _ = e ?? throw new ArgumentNullException(nameof(e));
+
+            if (type == BindingErrorType.None)
+                throw new ArgumentException("BindingErrorType may not be None", nameof(type));

            Error = Error != null ? new AggregateException(Error, e) : e;

--- a/src/Avalonia.Base/Data/BindingOperations.cs
+++ b/src/Avalonia.Base/Data/BindingOperations.cs
@ -2,8 +2,6 @@ using System;
 using System.Reactive.Disposables;
 using System.Reactive.Linq;

-#nullable enable
-
 namespace Avalonia.Data
 {
    public static class BindingOperations
--- a/src/Avalonia.Base/Data/BindingPriority.cs
+++ b/src/Avalonia.Base/Data/BindingPriority.cs
@ -1,5 +1,3 @@
-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/BindingValue.cs
+++ b/src/Avalonia.Base/Data/BindingValue.cs
@ -2,8 +2,6 @@
 using System.Diagnostics;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
@ -418,15 +416,15 @@ namespace Avalonia.Data
            {
                BindingValueType.DoNothing => BindingValue<T>.DoNothing,
                BindingValueType.UnsetValue => BindingValue<T>.Unset,
-                BindingValueType.Value => new BindingValue<T>(TypeUtilities.ConvertImplicit<T>(value.Value)),
+                BindingValueType.Value => new BindingValue<T>(TypeUtilities.ConvertImplicit<T>(value.Value!)),
                BindingValueType.BindingError => BindingValue<T>.BindingError(value.Error!),
                BindingValueType.BindingErrorWithFallback => BindingValue<T>.BindingError(
                        value.Error!,
-                        TypeUtilities.ConvertImplicit<T>(value.Value)),
+                        TypeUtilities.ConvertImplicit<T>(value.Value!)),
                BindingValueType.DataValidationError => BindingValue<T>.DataValidationError(value.Error!),
                BindingValueType.DataValidationErrorWithFallback => BindingValue<T>.DataValidationError(
                        value.Error!,
-                        TypeUtilities.ConvertImplicit<T>(value.Value)),
+                        TypeUtilities.ConvertImplicit<T>(value.Value!)),
                _ => throw new NotSupportedException("Invalid BindingValue type."),
            };
        }
--- a/src/Avalonia.Base/Data/Converters/BoolConverters.cs
+++ b/src/Avalonia.Base/Data/Converters/BoolConverters.cs
@ -1,7 +1,5 @@
 using System.Linq;

-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Converters/DefaultValueConverter.cs
+++ b/src/Avalonia.Base/Data/Converters/DefaultValueConverter.cs
@ -3,8 +3,6 @@ using System.Globalization;
 using System.Windows.Input;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    /// <summary>
@ -38,7 +36,7 @@ namespace Avalonia.Data.Converters
                return new MethodToCommandConverter(d);
            }

-            if (TypeUtilities.TryConvert(targetType, value, culture, out object result))
+            if (TypeUtilities.TryConvert(targetType, value, culture, out var result))
            {
                return result;
            }
--- a/src/Avalonia.Base/Data/Converters/FuncMultiValueConverter.cs
+++ b/src/Avalonia.Base/Data/Converters/FuncMultiValueConverter.cs
@ -3,8 +3,6 @@ using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;

-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Converters/FuncValueConverter.cs
+++ b/src/Avalonia.Base/Data/Converters/FuncValueConverter.cs
@ -2,8 +2,6 @@ using System;
 using System.Globalization;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Converters/IMultiValueConverter.cs
+++ b/src/Avalonia.Base/Data/Converters/IMultiValueConverter.cs
@ -2,8 +2,6 @@ using System;
 using System.Collections.Generic;
 using System.Globalization;

-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Converters/IValueConverter.cs
+++ b/src/Avalonia.Base/Data/Converters/IValueConverter.cs
@ -1,8 +1,6 @@
 using System;
 using System.Globalization;

-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Converters/MethodToCommandConverter.cs
+++ b/src/Avalonia.Base/Data/Converters/MethodToCommandConverter.cs
@ -7,19 +7,17 @@ using System.Reflection;
 using System.Windows.Input;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    class MethodToCommandConverter : ICommand
    {
-        readonly static Func<object, bool> AlwaysEnabled = (_) => true;
+        readonly static Func<object?, bool> AlwaysEnabled = (_) => true;
        readonly static MethodInfo tryConvert = typeof(TypeUtilities)
-            .GetMethod(nameof(TypeUtilities.TryConvert), BindingFlags.Public | BindingFlags.Static);
+            .GetMethod(nameof(TypeUtilities.TryConvert), BindingFlags.Public | BindingFlags.Static)!;
        readonly static PropertyInfo currentCulture = typeof(CultureInfo)
-            .GetProperty(nameof(CultureInfo.CurrentCulture), BindingFlags.Public | BindingFlags.Static);
-        readonly Func<object, bool> canExecute;
-        readonly Action<object> execute;
+            .GetProperty(nameof(CultureInfo.CurrentCulture), BindingFlags.Public | BindingFlags.Static)!;
+        readonly Func<object?, bool> canExecute;
+        readonly Action<object?> execute;
        readonly WeakPropertyChangedProxy? weakPropertyChanged;
        readonly PropertyChangedEventHandler? propertyChangedEventHandler;
        readonly string[]? dependencyProperties;
@ -40,7 +38,7 @@ namespace Avalonia.Data.Converters
                execute = CreateExecute(target, action.Method, parameterInfo);
            }

-            var canExecuteMethod = action.Method.DeclaringType.GetRuntimeMethods()
+            var canExecuteMethod = action.Method.DeclaringType?.GetRuntimeMethods()
                .FirstOrDefault(m => m.Name == canExecuteMethodName
                    && m.GetParameters().Length == 1
                    && m.GetParameters()[0].ParameterType == typeof(object));
@ -65,7 +63,7 @@ namespace Avalonia.Data.Converters
            }
        }

-        void OnPropertyChanged(object sender, PropertyChangedEventArgs args)
+        void OnPropertyChanged(object? sender, PropertyChangedEventArgs args)
        {
            if (string.IsNullOrWhiteSpace(args.PropertyName)
                               || dependencyProperties?.Contains(args.PropertyName) == true)
@ -79,12 +77,12 @@ namespace Avalonia.Data.Converters
        public event EventHandler? CanExecuteChanged;
 #pragma warning restore 0067

-        public bool CanExecute(object parameter) => canExecute(parameter);
+        public bool CanExecute(object? parameter) => canExecute(parameter);

-        public void Execute(object parameter) => execute(parameter);
+        public void Execute(object? parameter) => execute(parameter);


-        static Action<object> CreateExecute(object target
+        static Action<object?> CreateExecute(object? target
            , System.Reflection.MethodInfo method)
        {

@ -100,11 +98,11 @@ namespace Avalonia.Data.Converters


            return Expression
-                .Lambda<Action<object>>(call, parameter)
+                .Lambda<Action<object?>>(call, parameter)
                .Compile();
        }

-        static Action<object> CreateExecute(object target
+        static Action<object?> CreateExecute(object? target
            , System.Reflection.MethodInfo method
            , Type parameterType)
        {
@ -143,11 +141,11 @@ namespace Avalonia.Data.Converters

            }
            return Expression
-                .Lambda<Action<object>>(body, parameter)
+                .Lambda<Action<object?>>(body, parameter)
                .Compile();
        }

-        static Func<object, bool> CreateCanExecute(object target
+        static Func<object?, bool> CreateCanExecute(object? target
            , System.Reflection.MethodInfo method)
        {
            var parameter = Expression.Parameter(typeof(object), "parameter");
@ -159,12 +157,12 @@ namespace Avalonia.Data.Converters
                parameter
            );
            return Expression
-                .Lambda<Func<object, bool>>(call, parameter)
+                .Lambda<Func<object?, bool>>(call, parameter)
                .Compile();
        }

-        private static Expression? ConvertTarget(object target, MethodInfo method) =>
-            target is null ? null : Expression.Convert(Expression.Constant(target), method.DeclaringType);
+        private static Expression? ConvertTarget(object? target, MethodInfo method) =>
+            target is null ? null : Expression.Convert(Expression.Constant(target), method.DeclaringType!);

        internal class WeakPropertyChangedProxy
        {
@ -199,7 +197,7 @@ namespace Avalonia.Data.Converters
                _listener.SetTarget(null);
            }

-            void OnPropertyChanged(object sender, PropertyChangedEventArgs e)
+            void OnPropertyChanged(object? sender, PropertyChangedEventArgs e)
            {
                if (_listener.TryGetTarget(out var handler) && handler != null)
                    handler(sender, e);
--- a/src/Avalonia.Base/Data/Converters/ObjectConverters.cs
+++ b/src/Avalonia.Base/Data/Converters/ObjectConverters.cs
@ -1,5 +1,3 @@
-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Converters/StringConverters.cs
+++ b/src/Avalonia.Base/Data/Converters/StringConverters.cs
@ -1,5 +1,3 @@
-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Converters/StringFormatMultiValueConverter.cs
+++ b/src/Avalonia.Base/Data/Converters/StringFormatMultiValueConverter.cs
@ -3,8 +3,6 @@ using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;

-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Converters/StringFormatValueConverter.cs
+++ b/src/Avalonia.Base/Data/Converters/StringFormatValueConverter.cs
@ -1,8 +1,6 @@
 using System;
 using System.Globalization;

-#nullable enable
-
 namespace Avalonia.Data.Converters
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Core/AvaloniaPropertyAccessorNode.cs
+++ b/src/Avalonia.Base/Data/Core/AvaloniaPropertyAccessorNode.cs
@ -2,8 +2,6 @@
 using System.Reactive.Linq;
 using Avalonia.Reactive;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public class AvaloniaPropertyAccessorNode : SettableNode
--- a/src/Avalonia.Base/Data/Core/BindingExpression.cs
+++ b/src/Avalonia.Base/Data/Core/BindingExpression.cs
@ -7,8 +7,6 @@ using Avalonia.Logging;
 using Avalonia.Reactive;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    /// <summary>
@ -263,7 +261,7 @@ namespace Avalonia.Data.Core

        private BindingNotification ConvertFallback()
        {
-            object converted;
+            object? converted;

            if (_fallbackValue == AvaloniaProperty.UnsetValue)
            {
--- a/src/Avalonia.Base/Data/Core/ClrPropertyInfo.cs
+++ b/src/Avalonia.Base/Data/Core/ClrPropertyInfo.cs
@ -2,8 +2,6 @@ using System;
 using System.Linq.Expressions;
 using System.Reflection;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public class ClrPropertyInfo : IPropertyInfo
@ -49,7 +47,7 @@ namespace Avalonia.Data.Core
            var target = Expression.Parameter(typeof(object), "target");
            var value = Expression.Parameter(typeof(object), "value");
            return Expression.Lambda<Action<object, object?>>(
-                    Expression.Call(Expression.Convert(target, info.DeclaringType), info.SetMethod,
+                    Expression.Call(Expression.Convert(target, info.DeclaringType!), info.SetMethod,
                        Expression.Convert(value, info.SetMethod.GetParameters()[0].ParameterType)),
                    target, value)
                .Compile();
@ -61,7 +59,7 @@ namespace Avalonia.Data.Core
                return null;
            var target = Expression.Parameter(typeof(object), "target");
            return Expression.Lambda<Func<object, object>>(
-                    Expression.Convert(Expression.Call(Expression.Convert(target, info.DeclaringType), info.GetMethod),
+                    Expression.Convert(Expression.Call(Expression.Convert(target, info.DeclaringType!), info.GetMethod),
                        typeof(object)))
                .Compile();
        }
--- a/src/Avalonia.Base/Data/Core/CommonPropertyNames.cs
+++ b/src/Avalonia.Base/Data/Core/CommonPropertyNames.cs
@ -1,5 +1,3 @@
-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public static class CommonPropertyNames
--- a/src/Avalonia.Base/Data/Core/EmptyExpressionNode.cs
+++ b/src/Avalonia.Base/Data/Core/EmptyExpressionNode.cs
@ -1,6 +1,4 @@
-#nullable enable
-
-namespace Avalonia.Data.Core
+namespace Avalonia.Data.Core
 {
    public class EmptyExpressionNode : ExpressionNode
    {
--- a/src/Avalonia.Base/Data/Core/ExpressionNode.cs
+++ b/src/Avalonia.Base/Data/Core/ExpressionNode.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public abstract class ExpressionNode
--- a/src/Avalonia.Base/Data/Core/ExpressionObserver.cs
+++ b/src/Avalonia.Base/Data/Core/ExpressionObserver.cs
@ -7,8 +7,6 @@ using Avalonia.Data.Core.Parsers;
 using Avalonia.Data.Core.Plugins;
 using Avalonia.Reactive;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Core/ExpressionParseException.cs
+++ b/src/Avalonia.Base/Data/Core/ExpressionParseException.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Core/IPropertyInfo.cs
+++ b/src/Avalonia.Base/Data/Core/IPropertyInfo.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public interface IPropertyInfo
--- a/src/Avalonia.Base/Data/Core/ITransformNode.cs
+++ b/src/Avalonia.Base/Data/Core/ITransformNode.cs
@ -1,6 +1,4 @@
-#nullable enable
-
-namespace Avalonia.Data.Core
+namespace Avalonia.Data.Core
 {
    interface ITransformNode
    {
--- a/src/Avalonia.Base/Data/Core/IndexerExpressionNode.cs
+++ b/src/Avalonia.Base/Data/Core/IndexerExpressionNode.cs
@ -4,8 +4,6 @@ using System.ComponentModel;
 using System.Linq.Expressions;
 using System.Reflection;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    class IndexerExpressionNode : IndexerNodeBase
@ -18,7 +16,7 @@ namespace Avalonia.Data.Core

        public IndexerExpressionNode(IndexExpression expression)
        {
-            _parameter = Expression.Parameter(expression.Object.Type);
+            _parameter = Expression.Parameter(expression.Object!.Type);
            _expression = expression.Update(_parameter, expression.Arguments);

            _getDelegate = Expression.Lambda(_expression, _parameter).Compile();
--- a/src/Avalonia.Base/Data/Core/IndexerNodeBase.cs
+++ b/src/Avalonia.Base/Data/Core/IndexerNodeBase.cs
@ -7,8 +7,6 @@ using System.Linq;
 using System.Reactive.Linq;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public abstract class IndexerNodeBase : SettableNode
@ -72,12 +70,12 @@ namespace Avalonia.Data.Core
                        return index >= e.OldStartingIndex;
                    case NotifyCollectionChangedAction.Replace:
                        return index >= e.NewStartingIndex &&
-                               index < e.NewStartingIndex + e.NewItems.Count;
+                               index < e.NewStartingIndex + e.NewItems!.Count;
                    case NotifyCollectionChangedAction.Move:
                        return (index >= e.NewStartingIndex &&
-                                index < e.NewStartingIndex + e.NewItems.Count) ||
+                                index < e.NewStartingIndex + e.NewItems!.Count) ||
                               (index >= e.OldStartingIndex &&
-                                index < e.OldStartingIndex + e.OldItems.Count);
+                                index < e.OldStartingIndex + e.OldItems!.Count);
                    case NotifyCollectionChangedAction.Reset:
                        return true;
                }
--- a/src/Avalonia.Base/Data/Core/LogicalNotNode.cs
+++ b/src/Avalonia.Base/Data/Core/LogicalNotNode.cs
@ -1,8 +1,6 @@
 using System;
 using System.Globalization;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public class LogicalNotNode : ExpressionNode, ITransformNode
--- a/src/Avalonia.Base/Data/Core/MarkupBindingChainException.cs
+++ b/src/Avalonia.Base/Data/Core/MarkupBindingChainException.cs
@ -2,8 +2,6 @@
 using System.Collections.Generic;
 using System.Linq;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    internal class MarkupBindingChainException : BindingChainException
--- a/src/Avalonia.Base/Data/Core/Parsers/ExpressionTreeParser.cs
+++ b/src/Avalonia.Base/Data/Core/Parsers/ExpressionTreeParser.cs
@ -1,8 +1,6 @@
 using System.Linq;
 using System.Linq.Expressions;

-#nullable enable
-
 namespace Avalonia.Data.Core.Parsers
 {
    static class ExpressionTreeParser
--- a/src/Avalonia.Base/Data/Core/Parsers/ExpressionVisitorNodeBuilder.cs
+++ b/src/Avalonia.Base/Data/Core/Parsers/ExpressionVisitorNodeBuilder.cs
@ -4,8 +4,6 @@ using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;

-#nullable enable
-
 namespace Avalonia.Data.Core.Parsers
 {
    class ExpressionVisitorNodeBuilder : ExpressionVisitor
@ -18,8 +16,8 @@ namespace Avalonia.Data.Core.Parsers

        static ExpressionVisitorNodeBuilder()
        {
-            AvaloniaObjectIndexer = typeof(AvaloniaObject).GetProperty("Item", new[] { typeof(AvaloniaProperty) });
-            CreateDelegateMethod = typeof(MethodInfo).GetMethod("CreateDelegate", new[] { typeof(Type), typeof(object) });
+            AvaloniaObjectIndexer = typeof(AvaloniaObject).GetProperty("Item", new[] { typeof(AvaloniaProperty) })!;
+            CreateDelegateMethod = typeof(MethodInfo).GetMethod("CreateDelegate", new[] { typeof(Type), typeof(object) })!;
        }

        public List<ExpressionNode> Nodes { get; }
@ -164,7 +162,7 @@ namespace Avalonia.Data.Core.Parsers
            if (node.Method == CreateDelegateMethod)
            {
                var visited = Visit(node.Arguments[1]);
-                Nodes.Add(new PropertyAccessorNode(GetArgumentExpressionValue<MethodInfo>(node.Object).Name, _enableDataValidation));
+                Nodes.Add(new PropertyAccessorNode(GetArgumentExpressionValue<MethodInfo>(node.Object!).Name, _enableDataValidation));
                return node;
            }
            else if (node.Method.Name == StreamBindingExtensions.StreamBindingName || node.Method.Name.StartsWith(StreamBindingExtensions.StreamBindingName + '`'))
@ -185,20 +183,20 @@ namespace Avalonia.Data.Core.Parsers

            if (property != null)
            {
-                return Visit(Expression.MakeIndex(node.Object, property, node.Arguments));
+                return Visit(Expression.MakeIndex(node.Object!, property, node.Arguments));
            }
-            else if (node.Object.Type.IsArray && node.Method.Name == MultiDimensionalArrayGetterMethodName)
+            else if (node.Object!.Type.IsArray && node.Method.Name == MultiDimensionalArrayGetterMethodName)
            {
                return Visit(Expression.MakeIndex(node.Object, null, node.Arguments));
            }

-            throw new ExpressionParseException(0, $"Invalid method call in binding expression: '{node.Method.DeclaringType.AssemblyQualifiedName}.{node.Method.Name}'.");
+            throw new ExpressionParseException(0, $"Invalid method call in binding expression: '{node.Method.DeclaringType!.AssemblyQualifiedName}.{node.Method.Name}'.");
        }

-        private PropertyInfo TryGetPropertyFromMethod(MethodInfo method)
+        private PropertyInfo? TryGetPropertyFromMethod(MethodInfo method)
        {
            var type = method.DeclaringType;
-            return type.GetRuntimeProperties().FirstOrDefault(prop => prop.GetMethod == method);
+            return type?.GetRuntimeProperties().FirstOrDefault(prop => prop.GetMethod == method);
        }

        protected override Expression VisitSwitch(SwitchExpression node)
--- a/src/Avalonia.Base/Data/Core/Plugins/AvaloniaPropertyAccessorPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/AvaloniaPropertyAccessorPlugin.cs
@ -1,8 +1,6 @@
 using System;
 using System.Runtime.ExceptionServices;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
@ -74,12 +72,11 @@ namespace Avalonia.Data.Core.Plugins
                _property = property ?? throw new ArgumentNullException(nameof(property));
            }

-            public AvaloniaObject Instance
+            public AvaloniaObject? Instance
            {
                get
                {
-                    AvaloniaObject result;
-                    _reference.TryGetTarget(out result);
+                    _reference.TryGetTarget(out var result);
                    return result;
                }
            }
@ -91,7 +88,7 @@ namespace Avalonia.Data.Core.Plugins
            {
                if (!_property.IsReadOnly)
                {
-                    Instance.SetValue(_property, value, priority);
+                    Instance?.SetValue(_property, value, priority);
                    return true;
                }

--- a/src/Avalonia.Base/Data/Core/Plugins/DataAnnotationsValidationPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/DataAnnotationsValidationPlugin.cs
@ -4,8 +4,6 @@ using System.ComponentModel.DataAnnotations;
 using System.Linq;
 using System.Reflection;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
@ -33,19 +31,23 @@ namespace Avalonia.Data.Core.Plugins

        private sealed class Accessor : DataValidationBase
        {
-            private readonly ValidationContext _context;
+            private readonly ValidationContext? _context;

            public Accessor(WeakReference<object?> reference, string name, IPropertyAccessor inner)
                : base(inner)
            {
-                reference.TryGetTarget(out var target);
-
-                _context = new ValidationContext(target);
-                _context.MemberName = name;
+                if (reference.TryGetTarget(out var target))
+                {
+                    _context = new ValidationContext(target);
+                    _context.MemberName = name;
+                }
            }

            protected override void InnerValueChanged(object? value)
            {
+                if (_context is null)
+                    return;
+
                var errors = new List<ValidationResult>();

                if (Validator.TryValidateProperty(value, _context, errors))
--- a/src/Avalonia.Base/Data/Core/Plugins/DataValidationBase.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/DataValidationBase.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Core/Plugins/ExceptionValidationPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/ExceptionValidationPlugin.cs
@ -1,8 +1,6 @@
 using System;
 using System.Reflection;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
@ -32,7 +30,7 @@ namespace Avalonia.Data.Core.Plugins
                {
                    return base.SetValue(value, priority);
                }
-                catch (TargetInvocationException ex)
+                catch (TargetInvocationException ex) when (ex.InnerException is not null)
                {
                    PublishValue(new BindingNotification(ex.InnerException, BindingErrorType.DataValidationError));
                }
--- a/src/Avalonia.Base/Data/Core/Plugins/IDataValidationPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/IDataValidationPlugin.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Core/Plugins/IPropertyAccessor.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/IPropertyAccessor.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Core/Plugins/IPropertyAccessorPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/IPropertyAccessorPlugin.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Core/Plugins/IStreamPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/IStreamPlugin.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Core/Plugins/IndeiValidationPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/IndeiValidationPlugin.cs
@ -4,8 +4,6 @@ using System.ComponentModel;
 using System.Linq;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
@ -39,7 +37,7 @@ namespace Avalonia.Data.Core.Plugins
                _name = name;
            }

-            void IWeakSubscriber<DataErrorsChangedEventArgs>.OnEvent(object sender, DataErrorsChangedEventArgs e)
+            void IWeakSubscriber<DataErrorsChangedEventArgs>.OnEvent(object? sender, DataErrorsChangedEventArgs e)
            {
                if (e.PropertyName == _name || string.IsNullOrEmpty(e.PropertyName))
                {
--- a/src/Avalonia.Base/Data/Core/Plugins/InpcPropertyAccessorPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/InpcPropertyAccessorPlugin.cs
@ -4,8 +4,6 @@ using System.ComponentModel;
 using System.Reflection;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
@ -131,7 +129,7 @@ namespace Avalonia.Data.Core.Plugins
                return false;
            }

-            void IWeakSubscriber<PropertyChangedEventArgs>.OnEvent(object sender, PropertyChangedEventArgs e)
+            void IWeakSubscriber<PropertyChangedEventArgs>.OnEvent(object? sender, PropertyChangedEventArgs e)
            {
                if (e.PropertyName == _property.Name || string.IsNullOrEmpty(e.PropertyName))
                {
--- a/src/Avalonia.Base/Data/Core/Plugins/MethodAccessorPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/MethodAccessorPlugin.cs
@ -3,8 +3,6 @@ using System.Collections.Generic;
 using System.Linq.Expressions;
 using System.Reflection;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    public class MethodAccessorPlugin : IPropertyAccessorPlugin
--- a/src/Avalonia.Base/Data/Core/Plugins/ObservableStreamPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/ObservableStreamPlugin.cs
@ -3,8 +3,6 @@ using System.Linq;
 using System.Reactive.Linq;
 using System.Reflection;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
@ -57,14 +55,14 @@ namespace Avalonia.Data.Core.Plugins

            // Make a Box<> delegate of the correct type.
            var funcType = typeof(Func<,>).MakeGenericType(sourceType, typeof(object));
-            var box = GetType().GetMethod(nameof(Box), BindingFlags.Static | BindingFlags.NonPublic)
+            var box = GetType().GetMethod(nameof(Box), BindingFlags.Static | BindingFlags.NonPublic)!
                .MakeGenericMethod(sourceType)
                .CreateDelegate(funcType);

            // Call Observable.Select(target, box);
-            return (IObservable<object>)select.Invoke(
+            return (IObservable<object?>)select.Invoke(
                null,
-                new object[] { target, box });
+                new object[] { target, box })!;
        }

        private static MethodInfo GetObservableSelect(Type source)
--- a/src/Avalonia.Base/Data/Core/Plugins/PropertyAccessorBase.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/PropertyAccessorBase.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Core/Plugins/PropertyError.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/PropertyError.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Core/Plugins/TaskStreamPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/TaskStreamPlugin.cs
@ -4,8 +4,6 @@ using System.Reactive.Subjects;
 using System.Reflection;
 using System.Threading.Tasks;

-#nullable enable
-
 namespace Avalonia.Data.Core.Plugins
 {
    /// <summary>
@ -72,7 +70,7 @@ namespace Avalonia.Data.Core.Plugins
                    case TaskStatus.RanToCompletion:
                        return Observable.Return(resultProperty.GetValue(task));
                    case TaskStatus.Faulted:
-                        return Observable.Return(new BindingNotification(task.Exception, BindingErrorType.Error));
+                        return Observable.Return(new BindingNotification(task.Exception!, BindingErrorType.Error));
                    default:
                        throw new AvaloniaInternalException("HandleCompleted called for non-completed Task.");
                }
--- a/src/Avalonia.Base/Data/Core/PropertyAccessorNode.cs
+++ b/src/Avalonia.Base/Data/Core/PropertyAccessorNode.cs
@ -2,8 +2,6 @@ using System;
 using System.Diagnostics;
 using Avalonia.Data.Core.Plugins;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public class PropertyAccessorNode : SettableNode
--- a/src/Avalonia.Base/Data/Core/PropertyPath.cs
+++ b/src/Avalonia.Base/Data/Core/PropertyPath.cs
@ -2,8 +2,6 @@ using System;
 using System.Collections.Generic;
 using System.Linq;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public class PropertyPath
--- a/src/Avalonia.Base/Data/Core/SettableNode.cs
+++ b/src/Avalonia.Base/Data/Core/SettableNode.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public abstract class SettableNode : ExpressionNode
--- a/src/Avalonia.Base/Data/Core/StreamBindingExtensions.cs
+++ b/src/Avalonia.Base/Data/Core/StreamBindingExtensions.cs
@ -1,8 +1,6 @@
 using System;
 using System.Threading.Tasks;

-#nullable enable
-
 namespace Avalonia
 {
    public static class StreamBindingExtensions
--- a/src/Avalonia.Base/Data/Core/StreamNode.cs
+++ b/src/Avalonia.Base/Data/Core/StreamNode.cs
@ -2,8 +2,6 @@ using System;
 using System.Reactive.Linq;
 using Avalonia.Data.Core.Plugins;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public class StreamNode : ExpressionNode
--- a/src/Avalonia.Base/Data/Core/TypeCastNode.cs
+++ b/src/Avalonia.Base/Data/Core/TypeCastNode.cs
@ -2,8 +2,6 @@
 using System.Collections.Generic;
 using System.Text;

-#nullable enable
-
 namespace Avalonia.Data.Core
 {
    public class TypeCastNode : ExpressionNode
--- a/src/Avalonia.Base/Data/DataValidationException.cs
+++ b/src/Avalonia.Base/Data/DataValidationException.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/IBinding.cs
+++ b/src/Avalonia.Base/Data/IBinding.cs
@ -1,5 +1,3 @@
-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/IndexerBinding.cs
+++ b/src/Avalonia.Base/Data/IndexerBinding.cs
@ -1,6 +1,4 @@
-#nullable enable
-
-namespace Avalonia.Data
+namespace Avalonia.Data
 {
    public class IndexerBinding : IBinding
    {
--- a/src/Avalonia.Base/Data/IndexerDescriptor.cs
+++ b/src/Avalonia.Base/Data/IndexerDescriptor.cs
@ -1,8 +1,6 @@
 using System;
 using System.Reactive;

-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/InstancedBinding.cs
+++ b/src/Avalonia.Base/Data/InstancedBinding.cs
@ -1,8 +1,6 @@
 using System;
 using System.Reactive.Subjects;

-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
--- a/src/Avalonia.Base/Data/Optional.cs
+++ b/src/Avalonia.Base/Data/Optional.cs
@ -1,8 +1,6 @@
 using System;
 using System.Collections.Generic;

-#nullable enable
-
 namespace Avalonia.Data
 {
    /// <summary>
--- a/src/Avalonia.Base/Diagnostics/AvaloniaPropertyValue.cs
+++ b/src/Avalonia.Base/Diagnostics/AvaloniaPropertyValue.cs
@ -17,9 +17,9 @@ namespace Avalonia.Diagnostics
        /// <param name="diagnostic">A diagnostic string.</param>
        public AvaloniaPropertyValue(
            AvaloniaProperty property,
-            object value,
+            object? value,
            BindingPriority priority,
-            string diagnostic)
+            string? diagnostic)
        {
            Property = property;
            Value = value;
@ -35,7 +35,7 @@ namespace Avalonia.Diagnostics
        /// <summary>
        /// Gets the current property value.
        /// </summary>
-        public object Value { get; }
+        public object? Value { get; }

        /// <summary>
        /// Gets the priority of the current value.
@ -45,6 +45,6 @@ namespace Avalonia.Diagnostics
        /// <summary>
        /// Gets a diagnostic string.
        /// </summary>
-        public string Diagnostic { get; }
+        public string? Diagnostic { get; }
    }
 }
--- a/src/Avalonia.Base/Diagnostics/IAvaloniaObjectDebug.cs
+++ b/src/Avalonia.Base/Diagnostics/IAvaloniaObjectDebug.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia.Diagnostics
 {
    /// <summary>
--- a/src/Avalonia.Base/Diagnostics/INotifyCollectionChangedDebug.cs
+++ b/src/Avalonia.Base/Diagnostics/INotifyCollectionChangedDebug.cs
@ -17,6 +17,6 @@ namespace Avalonia.Diagnostics
        /// <returns>
        /// The subscribers or null if no subscribers.
        /// </returns>
-        Delegate[] GetCollectionChangedSubscribers();
+        Delegate[]? GetCollectionChangedSubscribers();
    }
 }
--- a/src/Avalonia.Base/DirectProperty.cs
+++ b/src/Avalonia.Base/DirectProperty.cs
@ -2,8 +2,6 @@ using System;
 using System.Diagnostics.CodeAnalysis;
 using Avalonia.Data;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/DirectPropertyBase.cs
+++ b/src/Avalonia.Base/DirectPropertyBase.cs
@ -3,8 +3,6 @@ using Avalonia.Data;
 using Avalonia.Reactive;
 using Avalonia.Utilities;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
@ -155,7 +153,7 @@ namespace Avalonia

            if (v.HasValue)
            {
-                o.SetValue<TValue>(this, (TValue)v.Value);
+                o.SetValue<TValue>(this, (TValue)v.Value!);
            }
            else if (v.Type == BindingValueType.UnsetValue)
            {
--- a/src/Avalonia.Base/DirectPropertyMetadata`1.cs
+++ b/src/Avalonia.Base/DirectPropertyMetadata`1.cs
@ -1,7 +1,5 @@
 using Avalonia.Data;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/EnumExtensions.cs
+++ b/src/Avalonia.Base/EnumExtensions.cs
@ -1,8 +1,6 @@
 using System;
 using System.Runtime.CompilerServices;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/IAvaloniaObject.cs
+++ b/src/Avalonia.Base/IAvaloniaObject.cs
@ -1,8 +1,6 @@
 using System;
 using Avalonia.Data;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/IDescription.cs
+++ b/src/Avalonia.Base/IDescription.cs
@ -1,5 +1,3 @@
-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/IDirectPropertyAccessor.cs
+++ b/src/Avalonia.Base/IDirectPropertyAccessor.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/IDirectPropertyMetadata.cs
+++ b/src/Avalonia.Base/IDirectPropertyMetadata.cs
@ -1,5 +1,3 @@
-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/IStyledPropertyAccessor.cs
+++ b/src/Avalonia.Base/IStyledPropertyAccessor.cs
@ -1,7 +1,5 @@
 using System;

-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>
--- a/src/Avalonia.Base/IStyledPropertyMetadata.cs
+++ b/src/Avalonia.Base/IStyledPropertyMetadata.cs
@ -1,5 +1,3 @@
-#nullable enable
-
 namespace Avalonia
 {
    /// <summary>