VectorClock inequality fixes

src/core/Akka.Cluster.Tests/VectorClockSpec.cs

@@ -29,6 +29,28 @@ public void A_VectorClock_must_not_happen_before_itself()
             (clock1 != clock2).Should().BeFalse();
         }
 
+        [Fact]
+        public void A_VectorClock_must_handle_null_equality_correctly()
+        {
+            VectorClock nullClock = null;
+            var clock = VectorClock.Create();
+
+            // null == null should be true
+            (nullClock == null).Should().BeTrue();
+            (null == nullClock).Should().BeTrue();
+
+            // null != null should be false
+            (nullClock != null).Should().BeFalse();
+
+            // clock == null and null == clock should be false
+            (clock == null).Should().BeFalse();
+            (null == clock).Should().BeFalse();
+
+            // clock != null and null != clock should be true
+            (clock != null).Should().BeTrue();
+            (null != clock).Should().BeTrue();
+        }
+
         [Fact]
         public void A_VectorClock_must_pass_misc_comparison_test1()
         {
@@ -60,6 +82,7 @@ public void A_VectorClock_must_pass_misc_comparison_test2()
             var clock5_2 = clock4_2.Increment(VectorClock.Node.Create("3"));
 
             (clock4_1 < clock5_2).Should().BeTrue();
+            (clock4_1 != clock5_2).Should().BeTrue("before relationship means not equal");
         }
 
         [Fact]
@@ -106,6 +129,8 @@ public void A_VectorClock_must_pass_misc_comparison_test5()
 
             (clock3_1 < clock5_2).Should().BeTrue();
             (clock5_2 > clock3_1).Should().BeTrue();
+            (clock3_1 != clock5_2).Should().BeTrue("before relationship means not equal");
+            (clock5_2 != clock3_1).Should().BeTrue("after relationship means not equal");
         }
 
         [Fact]

src/core/Akka.Cluster/VectorClock.cs

@@ -322,7 +322,9 @@ public bool IsSameAs(VectorClock that)
         /// <returns><c>true</c> if both vector clocks are equal; otherwise <c>false</c></returns>
         public static bool operator ==(VectorClock left, VectorClock right)
         {
-            if (ReferenceEquals(left, null))
+            if (ReferenceEquals(left, right))
+                return true;
+            if (ReferenceEquals(left, null) || ReferenceEquals(right, null))
                 return false;
 
             return left.IsSameAs(right);
@@ -336,10 +338,7 @@ public bool IsSameAs(VectorClock that)
         /// <returns><c>true</c> if both vector clocks are not equal; otherwise <c>false</c></returns>
         public static bool operator !=(VectorClock left, VectorClock right)
         {
-            if (ReferenceEquals(left, null))
-                return false;
-
-            return left.IsConcurrentWith(right);
+            return !(left == right);
         }
 
         private static readonly (Node, long) CmpEndMarker = (Node.Create("endmarker"), Timestamp.EndMarker);