Prohibit null values in map fields

On deserialization, missing values for message types
are replaced with a "default" message.

csharp/src/Google.Protobuf.Test/Collections/MapFieldTest.cs

@@ -56,7 +56,7 @@ namespace Google.Protobuf.Collections
         }
 
         [Test]
-        public void NullValues()
+        public void NullValuesProhibited()
         {
             TestNullValues<int?>(0);
             TestNullValues("");
@@ -65,19 +65,12 @@ namespace Google.Protobuf.Collections
 
         private void TestNullValues<T>(T nonNullValue)
         {
-            var map = new MapField<int, T>(false);
+            var map = new MapField<int, T>();
             var nullValue = (T) (object) null;
             Assert.Throws<ArgumentNullException>(() => map.Add(0, nullValue));
             Assert.Throws<ArgumentNullException>(() => map[0] = nullValue);
             map.Add(1, nonNullValue);
             map[1] = nonNullValue;
-
-            // Doesn't throw...
-            map = new MapField<int, T>(true);
-            map.Add(0, nullValue);
-            map[0] = nullValue;
-            map.Add(1, nonNullValue);
-            map[1] = nonNullValue;
         }
 
         [Test]
@@ -160,27 +153,6 @@ namespace Google.Protobuf.Collections
             EqualityTester.AssertInequality(map1, map2);
         }
 
-        [Test]
-        public void EqualityHandlesNullValues()
-        {
-            var map1 = new MapField<string, ForeignMessage>();
-            map1.Add("a", new ForeignMessage { C = 10 });
-            map1.Add("b", null);
-
-            var map2 = new MapField<string, ForeignMessage>();
-            map2.Add("a", new ForeignMessage { C = 10 });
-            map2.Add("b", null);
-
-            EqualityTester.AssertEquality(map1, map2);
-            // Check the null value isn't ignored entirely...
-            Assert.IsTrue(map1.Remove("b"));
-            EqualityTester.AssertInequality(map1, map2);
-            map1.Add("b", new ForeignMessage());
-            EqualityTester.AssertInequality(map1, map2);
-            map1["b"] = null;
-            EqualityTester.AssertEquality(map1, map2);
-        }
-
         [Test]
         public void Add_Dictionary()
         {
@@ -453,30 +425,6 @@ namespace Google.Protobuf.Collections
             Assert.Throws<ArgumentNullException>(() => dictionary["x"] = null);
         }
 
-        [Test]
-        public void AllowNullValues_Property()
-        {
-            // Non-message reference type values are non-nullable by default, but can be overridden
-            Assert.IsFalse(new MapField<int, string>().AllowsNullValues);
-            Assert.IsFalse(new MapField<int, string>(false).AllowsNullValues);
-            Assert.IsTrue(new MapField<int, string>(true).AllowsNullValues);
-
-            // Non-nullable value type values are never nullable
-            Assert.IsFalse(new MapField<int, int>().AllowsNullValues);
-            Assert.IsFalse(new MapField<int, int>(false).AllowsNullValues);
-            Assert.Throws<ArgumentException>(() => new MapField<int, int>(true));
-
-            // Message type values are nullable by default, but can be overridden
-            Assert.IsTrue(new MapField<int, TestAllTypes>().AllowsNullValues);
-            Assert.IsFalse(new MapField<int, TestAllTypes>(false).AllowsNullValues);
-            Assert.IsTrue(new MapField<int, TestAllTypes>(true).AllowsNullValues);
-
-            // Nullable value type values are nullable by default, but can be overridden
-            Assert.IsTrue(new MapField<int, int?>().AllowsNullValues);
-            Assert.IsFalse(new MapField<int, int?>(false).AllowsNullValues);
-            Assert.IsTrue(new MapField<int, int?>(true).AllowsNullValues);
-        }
-
         [Test]
         public void KeysReturnsLiveView()
         {

csharp/src/Google.Protobuf.Test/GeneratedMessageTest.cs

@@ -221,7 +221,7 @@ namespace Google.Protobuf
                 },
                 MapInt32ForeignMessage = {
                     { 0, new ForeignMessage { C = 10 } },
-                    { 5, null },
+                    { 5, new ForeignMessage() },
                 },
                 MapInt32Enum = {
                     { 1, MapEnum.MAP_ENUM_BAR },
@@ -268,6 +268,40 @@ namespace Google.Protobuf
             Assert.AreEqual(nestedMessage, parsed.MapInt32ForeignMessage[0]);
         }
 
+        [Test]
+        public void MapWithOnlyKey_PrimitiveValue()
+        {
+            // Hand-craft the stream to contain a single entry with just a key.
+            var memoryStream = new MemoryStream();
+            var output = new CodedOutputStream(memoryStream);
+            output.WriteTag(TestMap.MapInt32DoubleFieldNumber, WireFormat.WireType.LengthDelimited);
+            int key = 10;
+            output.WriteLength(1 + CodedOutputStream.ComputeInt32Size(key));
+            output.WriteTag(1, WireFormat.WireType.Varint);
+            output.WriteInt32(key);
+            output.Flush();
+
+            var parsed = TestMap.Parser.ParseFrom(memoryStream.ToArray());
+            Assert.AreEqual(0.0, parsed.MapInt32Double[key]);
+        }
+
+        [Test]
+        public void MapWithOnlyKey_MessageValue()
+        {
+            // Hand-craft the stream to contain a single entry with just a key.
+            var memoryStream = new MemoryStream();
+            var output = new CodedOutputStream(memoryStream);
+            output.WriteTag(TestMap.MapInt32ForeignMessageFieldNumber, WireFormat.WireType.LengthDelimited);
+            int key = 10;
+            output.WriteLength(1 + CodedOutputStream.ComputeInt32Size(key));
+            output.WriteTag(1, WireFormat.WireType.Varint);
+            output.WriteInt32(key);
+            output.Flush();
+
+            var parsed = TestMap.Parser.ParseFrom(memoryStream.ToArray());
+            Assert.AreEqual(new ForeignMessage(), parsed.MapInt32ForeignMessage[key]);
+        }
+
         [Test]
         public void MapIgnoresExtraFieldsWithinEntryMessages()
         {

csharp/src/Google.Protobuf.Test/JsonFormatterTest.cs

@@ -195,13 +195,6 @@ namespace Google.Protobuf
             AssertJson("{ 'repeatedForeignEnum': [ ] }", JsonFormatter.Default.Format(message));
         }
 
-        [Test]
-        public void NullValueForMessage()
-        {
-            var message = new TestMap { MapInt32ForeignMessage = { { 10, null } } };
-            AssertJson("{ 'mapInt32ForeignMessage': { '10': null } }", JsonFormatter.Default.Format(message));
-        }
-
         [Test]
         [TestCase("a\u17b4b", "a\\u17b4b")] // Explicit
         [TestCase("a\u0601b", "a\\u0601b")] // Ranged

csharp/src/Google.Protobuf.Test/TestProtos/UnittestWellKnownTypes.cs

@@ -2080,7 +2080,7 @@ namespace Google.Protobuf.TestProtos {
     public const int DoubleFieldFieldNumber = 10;
     private static readonly pbc::MapField<int, double?>.Codec _map_doubleField_codec
         = new pbc::MapField<int, double?>.Codec(pb::FieldCodec.ForInt32(8), pb::FieldCodec.ForStructWrapper<double>(18), 82);
-    private readonly pbc::MapField<int, double?> doubleField_ = new pbc::MapField<int, double?>(true);
+    private readonly pbc::MapField<int, double?> doubleField_ = new pbc::MapField<int, double?>();
     public pbc::MapField<int, double?> DoubleField {
       get { return doubleField_; }
     }
@@ -2089,7 +2089,7 @@ namespace Google.Protobuf.TestProtos {
     public const int FloatFieldFieldNumber = 11;
     private static readonly pbc::MapField<int, float?>.Codec _map_floatField_codec
         = new pbc::MapField<int, float?>.Codec(pb::FieldCodec.ForInt32(8), pb::FieldCodec.ForStructWrapper<float>(18), 90);
-    private readonly pbc::MapField<int, float?> floatField_ = new pbc::MapField<int, float?>(true);
+    private readonly pbc::MapField<int, float?> floatField_ = new pbc::MapField<int, float?>();
     public pbc::MapField<int, float?> FloatField {
       get { return floatField_; }
     }
@@ -2098,7 +2098,7 @@ namespace Google.Protobuf.TestProtos {
     public const int Int64FieldFieldNumber = 12;
     private static readonly pbc::MapField<int, long?>.Codec _map_int64Field_codec
         = new pbc::MapField<int, long?>.Codec(pb::FieldCodec.ForInt32(8), pb::FieldCodec.ForStructWrapper<long>(18), 98);
-    private readonly pbc::MapField<int, long?> int64Field_ = new pbc::MapField<int, long?>(true);
+    private readonly pbc::MapField<int, long?> int64Field_ = new pbc::MapField<int, long?>();
     public pbc::MapField<int, long?> Int64Field {
       get { return int64Field_; }
     }
@@ -2107,7 +2107,7 @@ namespace Google.Protobuf.TestProtos {
     public const int Uint64FieldFieldNumber = 13;
     private static readonly pbc::MapField<int, ulong?>.Codec _map_uint64Field_codec
         = new pbc::MapField<int, ulong?>.Codec(pb::FieldCodec.ForInt32(8), pb::FieldCodec.ForStructWrapper<ulong>(18), 106);
-    private readonly pbc::MapField<int, ulong?> uint64Field_ = new pbc::MapField<int, ulong?>(true);
+    private readonly pbc::MapField<int, ulong?> uint64Field_ = new pbc::MapField<int, ulong?>();
     public pbc::MapField<int, ulong?> Uint64Field {
       get { return uint64Field_; }
     }
@@ -2116,7 +2116,7 @@ namespace Google.Protobuf.TestProtos {
     public const int Int32FieldFieldNumber = 14;
     private static readonly pbc::MapField<int, int?>.Codec _map_int32Field_codec
         = new pbc::MapField<int, int?>.Codec(pb::FieldCodec.ForInt32(8), pb::FieldCodec.ForStructWrapper<int>(18), 114);
-    private readonly pbc::MapField<int, int?> int32Field_ = new pbc::MapField<int, int?>(true);
+    private readonly pbc::MapField<int, int?> int32Field_ = new pbc::MapField<int, int?>();
     public pbc::MapField<int, int?> Int32Field {
       get { return int32Field_; }
     }
@@ -2125,7 +2125,7 @@ namespace Google.Protobuf.TestProtos {
     public const int Uint32FieldFieldNumber = 15;
     private static readonly pbc::MapField<int, uint?>.Codec _map_uint32Field_codec
         = new pbc::MapField<int, uint?>.Codec(pb::FieldCodec.ForInt32(8), pb::FieldCodec.ForStructWrapper<uint>(18), 122);
-    private readonly pbc::MapField<int, uint?> uint32Field_ = new pbc::MapField<int, uint?>(true);
+    private readonly pbc::MapField<int, uint?> uint32Field_ = new pbc::MapField<int, uint?>();
     public pbc::MapField<int, uint?> Uint32Field {
       get { return uint32Field_; }
     }
@@ -2134,7 +2134,7 @@ namespace Google.Protobuf.TestProtos {
     public const int BoolFieldFieldNumber = 16;
     private static readonly pbc::MapField<int, bool?>.Codec _map_boolField_codec
         = new pbc::MapField<int, bool?>.Codec(pb::FieldCodec.ForInt32(8), pb::FieldCodec.ForStructWrapper<bool>(18), 130);
-    private readonly pbc::MapField<int, bool?> boolField_ = new pbc::MapField<int, bool?>(true);
+    private readonly pbc::MapField<int, bool?> boolField_ = new pbc::MapField<int, bool?>();
     public pbc::MapField<int, bool?> BoolField {
       get { return boolField_; }
     }
@@ -2143,7 +2143,7 @@ namespace Google.Protobuf.TestProtos {
     public const int StringFieldFieldNumber = 17;
     private static readonly pbc::MapField<int, string>.Codec _map_stringField_codec
         = new pbc::MapField<int, string>.Codec(pb::FieldCodec.ForInt32(8), pb::FieldCodec.ForClassWrapper<string>(18), 138);
-    private readonly pbc::MapField<int, string> stringField_ = new pbc::MapField<int, string>(true);
+    private readonly pbc::MapField<int, string> stringField_ = new pbc::MapField<int, string>();
     public pbc::MapField<int, string> StringField {
       get { return stringField_; }
     }
@@ -2152,7 +2152,7 @@ namespace Google.Protobuf.TestProtos {
     public const int BytesFieldFieldNumber = 18;
     private static readonly pbc::MapField<int, pb::ByteString>.Codec _map_bytesField_codec
         = new pbc::MapField<int, pb::ByteString>.Codec(pb::FieldCodec.ForInt32(8), pb::FieldCodec.ForClassWrapper<pb::ByteString>(18), 146);
-    private readonly pbc::MapField<int, pb::ByteString> bytesField_ = new pbc::MapField<int, pb::ByteString>(true);
+    private readonly pbc::MapField<int, pb::ByteString> bytesField_ = new pbc::MapField<int, pb::ByteString>();
     public pbc::MapField<int, pb::ByteString> BytesField {
       get { return bytesField_; }
     }

csharp/src/Google.Protobuf.Test/WellKnownTypes/WrappersTest.cs

@@ -151,6 +151,8 @@ namespace Google.Protobuf.WellKnownTypes
         [Test]
         public void MapWrappersSerializeDeserialize()
         {
+            // Note: no null values here, as they are prohibited in map fields
+            // (despite being representable).
             var message = new MapWellKnownTypes
             {
                 BoolField = { { 10, false }, { 20, true } },
@@ -158,13 +160,12 @@ namespace Google.Protobuf.WellKnownTypes
                     { -1, ByteString.CopyFrom(1, 2, 3) },
                     { 10, ByteString.CopyFrom(4, 5, 6) },
                     { 1000, ByteString.Empty },
-                    { 10000, null }
                 },
                 DoubleField = { { 1, 12.5 }, { 10, -1.5 }, { 20, 0d } },
                 FloatField = { { 2, 123.25f }, { 3, -20f }, { 4, 0f } },
                 Int32Field = { { 5, int.MaxValue }, { 6, int.MinValue }, { 7, 0 } },
                 Int64Field = { { 8, long.MaxValue }, { 9, long.MinValue }, { 10, 0L } },
-                StringField = { { 11, "First" }, { 12, "Second" }, { 13, "" }, { 14, null } },
+                StringField = { { 11, "First" }, { 12, "Second" }, { 13, "" } },
                 Uint32Field = { { 15, uint.MaxValue }, { 16, uint.MinValue }, { 17, 0U } },
                 Uint64Field = { { 18, ulong.MaxValue }, { 19, ulong.MinValue }, { 20, 0UL } },
             };
@@ -224,13 +225,11 @@ namespace Google.Protobuf.WellKnownTypes
         [Test]
         public void Reflection_MapFields()
         {
-            // Just a single example... note that we can't have a null value here
-            var message = new MapWellKnownTypes { Int32Field = { { 1, 2 }, { 3, null } } };
+            // Just a single example... note that we can't have a null value here despite the value type being int?
+            var message = new MapWellKnownTypes { Int32Field = { { 1, 2 } } };
             var fields = MapWellKnownTypes.Descriptor.Fields;
             var dictionary = (IDictionary) fields[MapWellKnownTypes.Int32FieldFieldNumber].Accessor.GetValue(message);
             Assert.AreEqual(2, dictionary[1]);
-            Assert.IsNull(dictionary[3]);
-            Assert.IsTrue(dictionary.Contains(3));
         }
 
         [Test]

csharp/src/Google.Protobuf/Collections/MapField.cs

@@ -53,6 +53,13 @@ namespace Google.Protobuf.Collections
     /// For string keys, the equality comparison is provided by <see cref="StringComparer.Ordinal" />.
     /// </para>
     /// <para>
+    /// Null values are not permitted in the map, either for wrapper types or regular messages.
+    /// If a map is deserialized from a data stream and the value is missing from an entry, a default value
+    /// is created instead. For primitive types, that is the regular default value (0, the empty string and so
+    /// on); for message types, an empty instance of the message is created, as if the map entry contained a 0-length
+    /// encoded value for the field.
+    /// </para>
+    /// <para>
     /// This implementation does not generally prohibit the use of key/value types which are not
     /// supported by Protocol Buffers (e.g. using a key type of <code>byte</code>) but nor does it guarantee
     /// that all operations will work in such cases.
@@ -61,34 +68,10 @@ namespace Google.Protobuf.Collections
     public sealed class MapField<TKey, TValue> : IDeepCloneable<MapField<TKey, TValue>>, IDictionary<TKey, TValue>, IEquatable<MapField<TKey, TValue>>, IDictionary
     {
         // TODO: Don't create the map/list until we have an entry. (Assume many maps will be empty.)
-        private readonly bool allowNullValues;
         private readonly Dictionary<TKey, LinkedListNode<KeyValuePair<TKey, TValue>>> map =
             new Dictionary<TKey, LinkedListNode<KeyValuePair<TKey, TValue>>>();
         private readonly LinkedList<KeyValuePair<TKey, TValue>> list = new LinkedList<KeyValuePair<TKey, TValue>>();
 
-        /// <summary>
-        /// Constructs a new map field, defaulting the value nullability to only allow null values for message types
-        /// and non-nullable value types.
-        /// </summary>
-        public MapField() : this(typeof(IMessage).IsAssignableFrom(typeof(TValue)) || Nullable.GetUnderlyingType(typeof(TValue)) != null)
-        {
-        }
-
-        /// <summary>
-        /// Constructs a new map field, overriding the choice of whether null values are permitted in the map.
-        /// This is used by wrapper types, where maps with string and bytes wrappers as the value types
-        /// support null values.
-        /// </summary>
-        /// <param name="allowNullValues">Whether null values are permitted in the map or not.</param>
-        public MapField(bool allowNullValues)
-        {
-            if (allowNullValues && typeof(TValue).IsValueType() && Nullable.GetUnderlyingType(typeof(TValue)) == null)
-            {
-                throw new ArgumentException("allowNullValues", "Non-nullable value types do not support null values");
-            }
-            this.allowNullValues = allowNullValues;
-        }
-
         /// <summary>
         /// Creates a deep clone of this object.
         /// </summary>
@@ -97,13 +80,13 @@ namespace Google.Protobuf.Collections
         /// </returns>
         public MapField<TKey, TValue> Clone()
         {
-            var clone = new MapField<TKey, TValue>(allowNullValues);
+            var clone = new MapField<TKey, TValue>();
             // Keys are never cloneable. Values might be.
             if (typeof(IDeepCloneable<TValue>).IsAssignableFrom(typeof(TValue)))
             {
                 foreach (var pair in list)
                 {
-                    clone.Add(pair.Key, pair.Value == null ? pair.Value : ((IDeepCloneable<TValue>)pair.Value).Clone());
+                    clone.Add(pair.Key, ((IDeepCloneable<TValue>)pair.Value).Clone());
                 }
             }
             else
@@ -217,7 +200,7 @@ namespace Google.Protobuf.Collections
             {
                 Preconditions.CheckNotNullUnconstrained(key, "key");
                 // value == null check here is redundant, but avoids boxing.
-                if (value == null && !allowNullValues)
+                if (value == null)
                 {
                     Preconditions.CheckNotNullUnconstrained(value, "value");
                 }
@@ -246,7 +229,7 @@ namespace Google.Protobuf.Collections
         public ICollection<TValue> Values { get { return new MapView<TValue>(this, pair => pair.Value, ContainsValue); } }
 
         /// <summary>
-        /// Adds the specified entries to the map.
+        /// Adds the specified entries to the map. The keys and values are not automatically cloned.
         /// </summary>
         /// <param name="entries">The entries to add to the map.</param>
         public void Add(IDictionary<TKey, TValue> entries)
@@ -346,11 +329,6 @@ namespace Google.Protobuf.Collections
             }
         }
 
-        /// <summary>
-        /// Returns whether or not this map allows values to be null.
-        /// </summary>
-        public bool AllowsNullValues { get { return allowNullValues; } }
-
         /// <summary>
         /// Gets the number of elements contained in the map.
         /// </summary>
@@ -632,6 +610,8 @@ namespace Google.Protobuf.Collections
             /// </summary>
             internal class MessageAdapter : IMessage
             {
+                private static readonly byte[] ZeroLengthMessageStreamData = new byte[] { 0 };
+
                 private readonly Codec codec;
                 internal TKey Key { get; set; }
                 internal TValue Value { get; set; }
@@ -665,6 +645,13 @@ namespace Google.Protobuf.Collections
                             input.SkipLastField();
                         }
                     }
+
+                    // Corner case: a map entry with a key but no value, where the value type is a message.
+                    // Read it as if we'd seen an input stream with no data (i.e. create a "default" message).
+                    if (Value == null)
+                    {
+                        Value = codec.valueCodec.Read(new CodedInputStream(ZeroLengthMessageStreamData));
+                    }
                 }
 
                 public void WriteTo(CodedOutputStream output)

csharp/src/Google.Protobuf/WellKnownTypes/Any.cs

@@ -61,8 +61,8 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   ///  If the embedded message type is well-known and has a custom JSON
   ///  representation, that representation will be embedded adding a field
-  ///  `value` which holds the custom JSON in addition to the the `@type`
-  ///  field. Example (for message [google.protobuf.Duration][google.protobuf.Duration]):
+  ///  `value` which holds the custom JSON in addition to the `@type`
+  ///  field. Example (for message [google.protobuf.Duration][]):
   ///
   ///      {
   ///        "@type": "type.googleapis.com/google.protobuf.Duration",
@@ -110,7 +110,7 @@ namespace Google.Protobuf.WellKnownTypes {
     ///  * If no schema is provided, `https` is assumed.
     ///  * The last segment of the URL's path must represent the fully
     ///    qualified name of the type (as in `path/google.protobuf.Duration`).
-    ///  * An HTTP GET on the URL must yield a [google.protobuf.Type][google.protobuf.Type]
+    ///  * An HTTP GET on the URL must yield a [google.protobuf.Type][]
     ///    value in binary format, or produce an error.
     ///  * Applications are allowed to cache lookup results based on the
     ///    URL, or have them precompiled into a binary to avoid any

csharp/src/Google.Protobuf/WellKnownTypes/Api.cs

@@ -653,7 +653,6 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   ///      package google.storage.v2;
   ///      service Storage {
-  ///        // (-- see AccessControl.GetAcl --)
   ///        rpc GetAcl(GetAclRequest) returns (Acl);
   ///
   ///        // Get a data record.

csharp/src/Google.Protobuf/WellKnownTypes/Empty.cs

@@ -24,9 +24,9 @@ namespace Google.Protobuf.WellKnownTypes {
       byte[] descriptorData = global::System.Convert.FromBase64String(
           string.Concat(
             "Chtnb29nbGUvcHJvdG9idWYvZW1wdHkucHJvdG8SD2dvb2dsZS5wcm90b2J1",
-            "ZiIHCgVFbXB0eUJNChNjb20uZ29vZ2xlLnByb3RvYnVmQgpFbXB0eVByb3Rv",
-            "UAGgAQGiAgNHUEKqAh5Hb29nbGUuUHJvdG9idWYuV2VsbEtub3duVHlwZXNi",
-            "BnByb3RvMw=="));
+            "ZiIHCgVFbXB0eUJQChNjb20uZ29vZ2xlLnByb3RvYnVmQgpFbXB0eVByb3Rv",
+            "UAGgAQH4AQGiAgNHUEKqAh5Hb29nbGUuUHJvdG9idWYuV2VsbEtub3duVHlw",
+            "ZXNiBnByb3RvMw=="));
       descriptor = pbr::FileDescriptor.FromGeneratedCode(descriptorData,
           new pbr::FileDescriptor[] { },
           new pbr::GeneratedCodeInfo(null, new pbr::GeneratedCodeInfo[] {

csharp/src/Google.Protobuf/WellKnownTypes/FieldMask.cs

@@ -69,7 +69,7 @@ namespace Google.Protobuf.WellKnownTypes {
   ///      z: 8
   ///
   ///  The result will not contain specific values for fields x,y and z
-  ///  (there value will be set to the default, and omitted in proto text
+  ///  (their value will be set to the default, and omitted in proto text
   ///  output):
   ///
   ///      f {

csharp/src/Google.Protobuf/WellKnownTypes/Timestamp.cs

@@ -25,9 +25,9 @@ namespace Google.Protobuf.WellKnownTypes {
           string.Concat(
             "Ch9nb29nbGUvcHJvdG9idWYvdGltZXN0YW1wLnByb3RvEg9nb29nbGUucHJv",
             "dG9idWYiKwoJVGltZXN0YW1wEg8KB3NlY29uZHMYASABKAMSDQoFbmFub3MY",
-            "AiABKAVCUQoTY29tLmdvb2dsZS5wcm90b2J1ZkIOVGltZXN0YW1wUHJvdG9Q",
-            "AaABAaICA0dQQqoCHkdvb2dsZS5Qcm90b2J1Zi5XZWxsS25vd25UeXBlc2IG",
-            "cHJvdG8z"));
+            "AiABKAVCVAoTY29tLmdvb2dsZS5wcm90b2J1ZkIOVGltZXN0YW1wUHJvdG9Q",
+            "AaABAfgBAaICA0dQQqoCHkdvb2dsZS5Qcm90b2J1Zi5XZWxsS25vd25UeXBl",
+            "c2IGcHJvdG8z"));
       descriptor = pbr::FileDescriptor.FromGeneratedCode(descriptorData,
           new pbr::FileDescriptor[] { },
           new pbr::GeneratedCodeInfo(null, new pbr::GeneratedCodeInfo[] {

csharp/src/Google.Protobuf/WellKnownTypes/Wrappers.cs

@@ -29,9 +29,10 @@ namespace Google.Protobuf.WellKnownTypes {
             "KAMiHAoLVUludDY0VmFsdWUSDQoFdmFsdWUYASABKAQiGwoKSW50MzJWYWx1",
             "ZRINCgV2YWx1ZRgBIAEoBSIcCgtVSW50MzJWYWx1ZRINCgV2YWx1ZRgBIAEo",
             "DSIaCglCb29sVmFsdWUSDQoFdmFsdWUYASABKAgiHAoLU3RyaW5nVmFsdWUS",
-            "DQoFdmFsdWUYASABKAkiGwoKQnl0ZXNWYWx1ZRINCgV2YWx1ZRgBIAEoDEJQ",
-            "ChNjb20uZ29vZ2xlLnByb3RvYnVmQg1XcmFwcGVyc1Byb3RvUAGgAQGiAgNH",
-            "UEKqAh5Hb29nbGUuUHJvdG9idWYuV2VsbEtub3duVHlwZXNiBnByb3RvMw=="));
+            "DQoFdmFsdWUYASABKAkiGwoKQnl0ZXNWYWx1ZRINCgV2YWx1ZRgBIAEoDEJT",
+            "ChNjb20uZ29vZ2xlLnByb3RvYnVmQg1XcmFwcGVyc1Byb3RvUAGgAQH4AQGi",
+            "AgNHUEKqAh5Hb29nbGUuUHJvdG9idWYuV2VsbEtub3duVHlwZXNiBnByb3Rv",
+            "Mw=="));
       descriptor = pbr::FileDescriptor.FromGeneratedCode(descriptorData,
           new pbr::FileDescriptor[] { },
           new pbr::GeneratedCodeInfo(null, new pbr::GeneratedCodeInfo[] {

src/google/protobuf/compiler/csharp/csharp_map_field.cc

@@ -62,7 +62,6 @@ void MapFieldGenerator::GenerateMembers(io::Printer* printer) {
       descriptor_->message_type()->FindFieldByName("value");
   variables_["key_type_name"] = type_name(key_descriptor);
   variables_["value_type_name"] = type_name(value_descriptor);
-  variables_["true_for_wrappers"] = IsWrapperType(value_descriptor) ? "true" : "";
   scoped_ptr<FieldGeneratorBase> key_generator(CreateFieldGenerator(key_descriptor, 1));  
   scoped_ptr<FieldGeneratorBase> value_generator(CreateFieldGenerator(value_descriptor, 2));
 
@@ -76,7 +75,7 @@ void MapFieldGenerator::GenerateMembers(io::Printer* printer) {
   printer->Print(
     variables_,
     ", $tag$);\n"
-    "private readonly pbc::MapField<$key_type_name$, $value_type_name$> $name$_ = new pbc::MapField<$key_type_name$, $value_type_name$>($true_for_wrappers$);\n");
+    "private readonly pbc::MapField<$key_type_name$, $value_type_name$> $name$_ = new pbc::MapField<$key_type_name$, $value_type_name$>();\n");
   WritePropertyDocComment(printer, descriptor_);
   AddDeprecatedFlag(printer);
   printer->Print(