From 8dfe6d5082ed5ca4bd9b270dd58a714beb100b01 Mon Sep 17 00:00:00 2001
From: Oliver Booth <me@olivr.me>
Date: Tue, 29 Nov 2022 17:26:03 +0000
Subject: [PATCH] Fix CS8600 and CS8602

---
 X10D/src/Drawing/Polygon.cs    | 6 ++++--
 X10D/src/Drawing/PolygonF.cs   | 4 +++-
 X10D/src/Drawing/Polyhedron.cs | 5 ++++-
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/X10D/src/Drawing/Polygon.cs b/X10D/src/Drawing/Polygon.cs
index 87c29bff8..f6564ad11 100644
--- a/X10D/src/Drawing/Polygon.cs
+++ b/X10D/src/Drawing/Polygon.cs
@@ -1,4 +1,5 @@
-using System.Drawing;
+using System.Diagnostics.CodeAnalysis;
+using System.Drawing;
 
 namespace X10D.Drawing;
 
@@ -128,7 +129,7 @@ public IReadOnlyList<Point> Vertices
     ///     <see langword="true" /> if <paramref name="left" /> and <paramref name="right" /> are considered not equal; otherwise,
     ///     <see langword="false" />.
     /// </returns>
-    public static bool operator !=(Polygon left, Polygon right)
+    public static bool operator !=(Polygon? left, Polygon? right)
     {
         return !(left == right);
     }
@@ -138,6 +139,7 @@ public IReadOnlyList<Point> Vertices
     /// </summary>
     /// <param name="polygon">The polygon to convert.</param>
     /// <returns>The converted polygon.</returns>
+    [return: NotNullIfNotNull("polygon")]
     public static explicit operator Polygon?(PolygonF? polygon)
     {
         return polygon is null ? null : FromPolygonF(polygon);
diff --git a/X10D/src/Drawing/PolygonF.cs b/X10D/src/Drawing/PolygonF.cs
index 13d7813c4..560f984a6 100644
--- a/X10D/src/Drawing/PolygonF.cs
+++ b/X10D/src/Drawing/PolygonF.cs
@@ -1,4 +1,5 @@
-using System.Drawing;
+using System.Diagnostics.CodeAnalysis;
+using System.Drawing;
 using System.Numerics;
 using X10D.Numerics;
 
@@ -169,6 +170,7 @@ public IReadOnlyList<PointF> Vertices
     /// </summary>
     /// <param name="polygon">The polygon to convert.</param>
     /// <returns>The converted polygon.</returns>
+    [return: NotNullIfNotNull("polygon")]
     public static implicit operator PolygonF?(Polygon? polygon)
     {
         return polygon is null ? null : FromPolygon(polygon);
diff --git a/X10D/src/Drawing/Polyhedron.cs b/X10D/src/Drawing/Polyhedron.cs
index 79a27cca4..15538fb5a 100644
--- a/X10D/src/Drawing/Polyhedron.cs
+++ b/X10D/src/Drawing/Polyhedron.cs
@@ -1,4 +1,5 @@
-using System.Drawing;
+using System.Diagnostics.CodeAnalysis;
+using System.Drawing;
 using System.Numerics;
 
 namespace X10D.Drawing;
@@ -140,6 +141,7 @@ public IReadOnlyList<Vector3> Vertices
     /// <returns>
     ///     The converted polyhedron, or <see langword="null" /> if <paramref name="polygon" /> is <see langword="null" />.
     /// </returns>
+    [return: NotNullIfNotNull("polygon")]
     public static implicit operator Polyhedron?(Polygon? polygon)
     {
         return polygon is null ? null : FromPolygon(polygon);
@@ -152,6 +154,7 @@ public IReadOnlyList<Vector3> Vertices
     /// <returns>
     ///     The converted polyhedron, or <see langword="null" /> if <paramref name="polygon" /> is <see langword="null" />.
     /// </returns>
+    [return: NotNullIfNotNull("polygon")]
     public static implicit operator Polyhedron?(PolygonF? polygon)
     {
         return polygon is null ? null : FromPolygonF(polygon);