DashStyle.Dashes is marked as nullable.

src/Avalonia.Base/Media/DashStyle.cs

@@ -17,8 +17,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="Dashes"/> property.
         /// </summary>
-        public static readonly StyledProperty<AvaloniaList<double>> DashesProperty =
-            AvaloniaProperty.Register<DashStyle, AvaloniaList<double>>(nameof(Dashes));
+        public static readonly StyledProperty<AvaloniaList<double>?> DashesProperty =
+            AvaloniaProperty.Register<DashStyle, AvaloniaList<double>?>(nameof(Dashes));
 
         /// <summary>
         /// Defines the <see cref="Offset"/> property.
@@ -83,7 +83,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets or sets the length of alternating dashes and gaps.
         /// </summary>
-        public AvaloniaList<double> Dashes
+        public AvaloniaList<double>? Dashes
         {
             get => GetValue(DashesProperty);
             set => SetValue(DashesProperty, value);
@@ -98,7 +98,7 @@ namespace Avalonia.Media
             set => SetValue(OffsetProperty, value);
         }
 
-        IReadOnlyList<double> IDashStyle.Dashes => Dashes;
+        IReadOnlyList<double>? IDashStyle.Dashes => Dashes;
 
         /// <summary>
         /// Raised when the dash style changes.

src/Avalonia.Base/Media/IDashStyle.cs

@@ -12,7 +12,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets or sets the length of alternating dashes and gaps.
         /// </summary>
-        IReadOnlyList<double> Dashes { get; }
+        IReadOnlyList<double>? Dashes { get; }
 
         /// <summary>
         /// Gets or sets how far in the dash sequence the stroke will start.

src/Avalonia.Base/Media/Immutable/ImmutableDashStyle.cs

@@ -17,7 +17,7 @@ namespace Avalonia.Media.Immutable
         /// </summary>
         /// <param name="dashes">The dashes collection.</param>
         /// <param name="offset">The dash sequence offset.</param>
-        public ImmutableDashStyle(IEnumerable<double> dashes, double offset)
+        public ImmutableDashStyle(IEnumerable<double>? dashes, double offset)
         {
             _dashes = dashes?.ToArray() ?? Array.Empty<double>();
             Offset = offset;
@@ -69,7 +69,7 @@ namespace Avalonia.Media.Immutable
             return hashCode;
         }
 
-        private static bool SequenceEqual(IReadOnlyList<double> left, IReadOnlyList<double> right)
+        private static bool SequenceEqual(IReadOnlyList<double> left, IReadOnlyList<double>? right)
         {
             if (ReferenceEquals(left, right))
             {