Fix nullable struct serialization

Addresses #360

Author: pensono

YamlDotNet.Test/Serialization/SerializationTestHelper.cs

@@ -141,6 +141,11 @@ public enum EnumExample
         Two
     }
 
+    public struct StructExample
+    {
+        public int Value { get; set; }
+    }
+
     public enum SByteEnum : sbyte { Default, Sbyte }
     public enum ByteEnum : byte { Default, Byte }
     public enum Int16Enum : short { Default, Short }

YamlDotNet.Test/Serialization/SerializationTests.cs

@@ -183,6 +183,24 @@ public void RoundtripNullableEnums(EnumExample? value)
             result.Should().Be(value);
         }
 
+        [Fact]
+        public void RoundtripNullableStructWithValue()
+        {
+            var value = new StructExample { Value = 2 };
+
+            var result = DoRoundtripFromObjectTo<StructExample?>(value);
+
+            result.Should().Be(value);
+        }
+
+        [Fact]
+        public void RoundtripNullableStructWithoutValue()
+        {
+            var result = DoRoundtripFromObjectTo<StructExample?>(null);
+
+            result.Should().Be(null);
+        }
+
         [Fact]
         public void SerializeCircularReference()
         {

YamlDotNet/Serialization/NodeDeserializers/ObjectNodeDeserializer.cs

@@ -47,11 +47,14 @@ bool INodeDeserializer.Deserialize(IParser parser, Type expectedType, Func<IPars
                 return false;
             }
 
-            value = objectFactory.Create(expectedType);
+            // Strip off the nullable type, if present. This is needed for nullable structs.
+            var implementationType = Nullable.GetUnderlyingType(expectedType) ?? expectedType;
+
+            value = objectFactory.Create(implementationType);
             while (!parser.TryConsume<MappingEnd>(out var _))
             {
                 var propertyName = parser.Consume<Scalar>();
-                var property = typeDescriptor.GetProperty(expectedType, null, propertyName.Value, ignoreUnmatched);
+                var property = typeDescriptor.GetProperty(implementationType, null, propertyName.Value, ignoreUnmatched);
                 if (property == null)
                 {
                     parser.SkipThisAndNestedEvents();