Fix nullable porperties serialization exception in EntryConvert

src/Moryx/Serialization/EntryConvert/EntryConvert.cs

@@ -126,10 +126,14 @@ private static EntryValue CreateEntryValue(PropertyInfo property, ICustomSeriali
                 entryValue.Default = defaultAttribute.Value.ToString();
             else if (entryValue.Possible != null && entryValue.Possible.Length >= 1)
                 entryValue.Default = entryValue.Possible[0];
-            else if (property.PropertyType.IsValueType)
-                entryValue.Default = Activator.CreateInstance(property.PropertyType).ToString();
-
-            // Value types should have the default value as current value
+            else if (property.PropertyType.IsValueType)
+            {
+                var underlyingType = Nullable.GetUnderlyingType(property.PropertyType);
+                entryValue.Default = underlyingType != null 
+                    ? Activator.CreateInstance(underlyingType).ToString() 
+                    : Activator.CreateInstance(property.PropertyType).ToString();
+            }
+            // Value types should have the default value as current value
             if (ValueOrStringType(property.PropertyType))
                 entryValue.Current = ConvertToString(entryValue.Default, customSerialization.FormatProvider);
 
@@ -312,7 +316,7 @@ public static Entry EncodeObject(object instance, ICustomSerialization customSer
                         convertedProperty.Value.Current = ConvertToString(subEntry.Value.Current, customSerialization.FormatProvider);
                         convertedProperty.SubEntries = subEntry.SubEntries;
                         break;
-                    case EntryValueType.Exception:
+                    case EntryValueType.Exception:
                         convertedProperty.Value.Current = ExceptionPrinter.Print((Exception)value);
                         break;
                     case EntryValueType.Stream:

src/Moryx/Serialization/EntryConvert/EntryConvertGenerator.cs

@@ -55,7 +55,7 @@ public static EntryValueType TransformType(Type propertyType)
             else if (propertyType == typeof(Double))
             {
                 valueType = EntryValueType.Double;
-            }
+            }
             else if (propertyType.IsEnum)
             {
                 valueType = EntryValueType.Enum;

src/Tests/Moryx.Tests/Serialization/DummyClass.cs

@@ -53,4 +53,9 @@ public enum DummyEnum
         ValueA,
         ValueB
     }
+
+    public class NullablePropertiesClass
+    {
+        public int? Value { get; set; } = 0;
+    }
 }

src/Tests/Moryx.Tests/Serialization/SerializationTests.cs

@@ -855,6 +855,14 @@ public void MemoryStreamDecodeReuseCurrentStreamInitSizeIsGreaterThanNewData()
             Assert.AreSame(streamInstanceToCheck, targetStreamDummy.MemoryStream);
         }
 
+        [Test(Description = "Testing nullable properties")]
+        public void NullableProperty()
+        {
+            var nullablePropertiesObject = new NullablePropertiesClass();
+
+            Assert.DoesNotThrow(() => EntryConvert.EncodeObject(nullablePropertiesObject));
+        }
+
         [Test(Description = "Encodes a FileStream")]
         public void FileStreamEncode()
         {