Fix SqlCommand.Cancell null ref exception

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlCommand.cs

@@ -1068,7 +1068,7 @@ public override void Cancel()
                 "SqlCommand.Cancel | API | Correlation | " +
                 $"Object Id {ObjectID}, " +
                 $"Activity Id {ActivityCorrelator.Current}, " +
-                $"Client Connection Id {_activeConnection.ClientConnectionId}, " +
+                $"Client Connection Id {_activeConnection?.ClientConnectionId}, " +
                 $"Command Text '{CommandText}'");
 
             SqlStatistics statistics = null;

src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlCommandTest.cs

@@ -562,6 +562,20 @@ public void ParameterCollectionTest()
             }
         }
 
+        /// <summary>
+        /// Verifies that SqlCommand.Cancel() is a no-op when Connection is null,
+        /// rather than throwing a NullReferenceException. Regression test for #4327.
+        /// </summary>
+        [Fact]
+        public void Cancel_WithNullConnection_DoesNotThrow()
+        {
+            using SqlCommand cmd = new SqlCommand();
+            Assert.Null(cmd.Connection);
+
+            // Should be a no-op, not throw NullReferenceException
+            cmd.Cancel();
+        }
+
         private static SqlConnection GetNonConnectingConnection() =>
             new SqlConnection("Initial Catalog=a;Server=b;User ID=c;Password=d");
     }