fixed bug with Code property and added tests.

Author: craiggwilson

MongoDB.Driver/CommandResults/CommandResult.cs

@@ -55,7 +55,7 @@ public CommandResult(IMongoCommand command, BsonDocument response)
         /// </summary>
         public int? Code
         {
-            get { return _response.GetValue("code", null).AsNullableInt32; }
+            get { return _response.GetValue("code", BsonNull.Value).AsNullableInt32; }
         }
 
         /// <summary>

MongoDB.DriverUnitTests/CommandResults/CommandResultTests.cs

@@ -33,6 +33,27 @@ public void Setup()
             _database = Configuration.TestDatabase;
         }
 
+        [Test]
+        public void TestCodeMissing()
+        {
+            var command = new CommandDocument("invalid", 1);
+            var document = new BsonDocument();
+            var result = new CommandResult(command, document);
+
+            Assert.IsFalse(result.Code.HasValue);
+        }
+
+        [Test]
+        public void TestCode()
+        {
+            var command = new CommandDocument("invalid", 1);
+            var document = new BsonDocument("code", 18);
+            var result = new CommandResult(command, document);
+
+            Assert.IsTrue(result.Code.HasValue);
+            Assert.AreEqual(18, result.Code);
+        }
+
         [Test]
         public void TestOkMissing()
         {