Add test +fix for null dictionary propertys.

Author: lanwin

source/MongoDB.Tests/UnitTests/Serialization/SerializationFactoryTests.cs

@@ -346,9 +346,20 @@ public void CanDeserializeADictionaryWithEnumAsKey()
             Assert.AreEqual(9,prop.Dict[DateTimeKind.Utc]);
         }
 
-        public class DictionaryWithEnumAsValueHelper
+        public class NullDictionaryPropertyHelper
         {
-            public Dictionary<int,DateTimeKind> Dict { get; set; }
+            public Dictionary<string, string> Dict { get; set; }
         }
+
+        [Test]
+        public void CanDeserializeAndNullDictionaryProperty()
+        {
+            var bson = Serialize<Document>(new Document("Dict", null));
+            var prop = Deserialize<NullDictionaryPropertyHelper>(bson);
+
+            Assert.IsNotNull(prop);
+            Assert.IsNull(prop.Dict);
+        }
+
     }
 }

source/MongoDB/Configuration/DictionaryAdapters/GenericDictionaryDictionaryAdapter.cs

@@ -35,6 +35,9 @@ public Type ValueType
         /// <returns></returns>
         public object CreateDictionary(Document document)
         {
+            if(document==null)
+                return null;
+
             return document.ToDictionary(pair => (TKey)ValueConverter.Convert(pair.Key, typeof(TKey)), pair => (TValue)pair.Value);
         }
 

source/MongoDB/Configuration/DictionaryAdapters/GenericSortedListDictionaryAdapter.cs

@@ -34,6 +34,9 @@ public Type ValueType
         /// <returns></returns>
         public object CreateDictionary(Document document)
         {
+            if(document == null)
+                return null;
+
             var list = new SortedList<TKey, TValue>();
 
             foreach(var pair in document)

source/MongoDB/Configuration/DictionaryAdapters/HashtableDictionaryAdapter.cs

@@ -34,6 +34,9 @@ public Type ValueType
         /// <returns></returns>
         public object CreateDictionary(Document document)
         {
+            if(document == null)
+                return null;
+
             var hashtable = new Hashtable();
 
             foreach (var pair in document)