Fix nullable porperties serialization exception in EntryConvert

`EntryConvertGenerator.TransformType()` returns `EntryValueType.Exception`
if `propertyType` parameter is nullable primitive type.

Author: DosenSuppe

src/Moryx/Serialization/EntryConvert/EntryConvert.cs

@@ -111,10 +111,12 @@ private static EntryValue CreateEntryValue(PropertyInfo property, ICustomSeriali
                 isReadOnly = readOnlyAtt?.IsReadOnly ?? false;
             }
 
+            var type = TransformType(property.PropertyType);
+
             // Prepare object
             var entryValue = new EntryValue
             {
-                Type = TransformType(property.PropertyType),
+                Type = type,
                 UnitType = customSerialization.GetUnitTypeByAttributes(property),
                 IsReadOnly = isReadOnly,
                 Possible = customSerialization.PossibleValues(property.PropertyType, property)
@@ -127,9 +129,9 @@ private static EntryValue CreateEntryValue(PropertyInfo property, ICustomSeriali
             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
+                entryValue.Default = 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);
 
@@ -313,7 +315,10 @@ public static Entry EncodeObject(object instance, ICustomSerialization customSer
                         convertedProperty.SubEntries = subEntry.SubEntries;
                         break;
                     case EntryValueType.Exception:
-                        convertedProperty.Value.Current = ExceptionPrinter.Print((Exception)value);
+                        if (value is Exception exceptionValue)
+                        {
+                            convertedProperty.Value.Current = ExceptionPrinter.Print(exceptionValue);
+                        }
                         break;
                     case EntryValueType.Stream:
                         var stream = value as Stream;

src/Moryx/Serialization/EntryConvert/EntryConvertGenerator.cs

@@ -15,7 +15,7 @@ public static partial class EntryConvert
         /// <returns>Enum representation of the property type</returns>
         public static EntryValueType TransformType(Type propertyType)
         {
-            var valueType = EntryValueType.String;
+            var valueType = EntryValueType.Exception;
             if (propertyType == typeof(Byte))
             {
                 valueType = EntryValueType.Byte;
@@ -56,6 +56,10 @@ public static EntryValueType TransformType(Type propertyType)
             {
                 valueType = EntryValueType.Double;
             }
+            else if (propertyType == typeof(String) || propertyType == typeof(string))
+            {
+                valueType = EntryValueType.String;
+            }
             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 +855,16 @@ public void MemoryStreamDecodeReuseCurrentStreamInitSizeIsGreaterThanNewData()
             Assert.AreSame(streamInstanceToCheck, targetStreamDummy.MemoryStream);
         }
 
+        [Test(Description = "Testing nullable properties")]
+        public void NullableProperty()
+        {
+            var nullablePropertiesObject = new NullablePropertiesClass();
+            
+            var result = EntryConvert.EncodeObject(nullablePropertiesObject);
+
+            Assert.AreEqual(EntryValueType.Exception, result.SubEntries[0].Value.Type);
+        }
+
         [Test(Description = "Encodes a FileStream")]
         public void FileStreamEncode()
         {