CSHARP-564: fix serialization of properties declared as an interface and having a value of null.

Author: rstam

Bson/Serialization/BsonClassMapSerializer.cs

@@ -473,19 +473,30 @@ private void DeserializeMember(BsonReader bsonReader, object obj, BsonMemberMap
         {
             try
             {
+                object value;
+
                 var nominalType = memberMap.MemberType;
-                Type actualType;
-                if (bsonReader.GetCurrentBsonType() == BsonType.Null)
+                var bsonType = bsonReader.GetCurrentBsonType();
+                if (bsonType == BsonType.Null && nominalType.IsInterface)
                 {
-                    actualType = nominalType;
+                    bsonReader.ReadNull();
+                    value = null;
                 }
-                else
-                {
-                    var discriminatorConvention = memberMap.GetDiscriminatorConvention();
-                    actualType = discriminatorConvention.GetActualType(bsonReader, nominalType); // returns nominalType if no discriminator found
+                else{
+                    Type actualType;
+                    if (bsonType == BsonType.Null)
+                    {
+                        actualType = nominalType;
+                    }
+                    else
+                    {
+                        var discriminatorConvention = memberMap.GetDiscriminatorConvention();
+                        actualType = discriminatorConvention.GetActualType(bsonReader, nominalType); // returns nominalType if no discriminator found
+                    }
+                    var serializer = memberMap.GetSerializer(actualType);
+                    value = serializer.Deserialize(bsonReader, nominalType, actualType, memberMap.SerializationOptions);
                 }
-                var serializer = memberMap.GetSerializer(actualType);
-                var value = serializer.Deserialize(bsonReader, nominalType, actualType, memberMap.SerializationOptions);
+
                 memberMap.Setter(obj, value);
             }
             catch (Exception ex)
@@ -541,10 +552,18 @@ private void SerializeMember(BsonWriter bsonWriter, object obj, BsonMemberMap me
             }
 
             bsonWriter.WriteName(memberMap.ElementName);
+
             var nominalType = memberMap.MemberType;
-            var actualType = (value == null) ? nominalType : value.GetType();
-            var serializer = memberMap.GetSerializer(actualType);
-            serializer.Serialize(bsonWriter, nominalType, value, memberMap.SerializationOptions);
+            if (value == null && nominalType.IsInterface)
+            {
+                bsonWriter.WriteNull();
+            }
+            else
+            {
+                var actualType = (value == null) ? nominalType : value.GetType();
+                var serializer = memberMap.GetSerializer(actualType);
+                serializer.Serialize(bsonWriter, nominalType, value, memberMap.SerializationOptions);
+            }
         }
 
         private void VerifyNominalType(Type nominalType)

BsonUnitTests/BsonUnitTests.csproj

@@ -151,6 +151,7 @@
     <Compile Include="Jira\CSharp467Tests.cs" />
     <Compile Include="Jira\CSharp479Tests.cs" />
     <Compile Include="Jira\CSharp515Tests.cs" />
+    <Compile Include="Jira\CSharp564Tests.cs" />
     <Compile Include="Jira\CSharp70Tests.cs" />
     <Compile Include="Jira\CSharp71Tests.cs" />
     <Compile Include="Jira\CSharp74Tests.cs" />

BsonUnitTests/Jira/CSharp564Tests.cs

@@ -0,0 +1,62 @@
+/* Copyright 2010-2012 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using NUnit.Framework;
+
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization;
+
+namespace MongoDB.BsonUnitTests.Jira.CSharp564
+{
+    [TestFixture]
+    public class CSharp564Tests
+    {
+        interface IWhatever { }
+        class Whatever : IWhatever { }
+
+        class Person
+        {
+            public IWhatever Whatever { get; set; }
+        }
+
+        [Test]
+        public void TestPersonWhateverNull()
+        {
+            var p = new Person();
+            var json = p.ToJson();
+            var expected = "{ 'Whatever' : null }".Replace("'", "\"");
+            Assert.AreEqual(expected, json);
+
+            var r = BsonSerializer.Deserialize<Person>(json);
+            Assert.AreEqual(null, r.Whatever);
+        }
+
+        [Test]
+        public void TestPersonWhateverNotNull()
+        {
+            var p = new Person() { Whatever = new Whatever() };
+            var json = p.ToJson();
+            var expected = "{ 'Whatever' : { '_t' : 'Whatever' } }".Replace("'", "\"");
+            Assert.AreEqual(expected, json);
+
+            var r = BsonSerializer.Deserialize<Person>(json);
+            Assert.IsInstanceOf<Whatever>(r.Whatever);
+        }
+    }
+}