equals handles null

src/GShark.Test.XUnit/Geometry/Point3Tests.cs

@@ -153,6 +153,38 @@ public void It_Returns_True_If_Two_Points_Are_Equal()
             (p1 == p2).Should().BeTrue();
         }
 
+        [Fact]
+        public void It_Returns_True_If_Two_Points_Are_Equal_Null_Case1()
+        {
+            // Arrange
+            Point3 p1 = new Point3(5.982099, 5.950299, 0);
+            Point3 p2 = null;
+
+            // Assert
+            (p1 == p2).Should().BeFalse();
+        }
+
+        [Fact]
+        public void It_Returns_True_If_Two_Points_Are_Equal_Null_Case2()
+        {
+            // Arrange
+            Point3 p1 = null;
+            Point3 p2 = new Point3(5.982099, 5.950299, 0);
+
+            // Assert
+            (p1 == p2).Should().BeFalse();
+        }
+        [Fact]
+        public void It_Returns_True_If_Two_Points_Are_Equal_Null_Case3()
+        {
+            // Arrange
+            Point3 p1 = null;
+            Point3 p2 = null;
+
+            // Assert
+            (p1 == p2).Should().BeFalse();
+        }
+
         [Fact]
         public void It_Returns_Whether_A_Point_Is_Inside_Outside_Or_Coincident_With_A_Polygon()
         {

src/GShark/Geometry/Point3.cs

@@ -198,6 +198,12 @@ public static Point3 Add(Vector3 vector, Point3 point)
         /// <returns>true if the coordinates of the two points are exactly equal; otherwise false.</returns>
         public static bool operator ==(Point3 a, Point3 b)
         {
+            if (a == null && b == null)
+                return true;
+            if (a == null || b == null)
+                return false;
+            if (ReferenceEquals(a, b))
+                return true;
             return (Math.Abs(a.X - b.X) < GSharkMath.MaxTolerance
                     && Math.Abs(a.Y - b.Y) < GSharkMath.MaxTolerance
                     && Math.Abs(a.Z - b.Z) < GSharkMath.MaxTolerance);
@@ -384,6 +390,14 @@ public double this[int i]
         /// <returns>true if obj is a Point3 and has the same coordinates as this; otherwise false.</returns>
         public override bool Equals(object obj)
         {
+            if (obj == null)
+                return false;
+
+            if (ReferenceEquals(this, obj))
+                return true;
+
+            if (this.GetType() != obj.GetType())
+                return false;
             return obj is Point3 point3 && this == point3;
         }