Add Nullable (to Value Types) at TypeReaders

src/Discord.Net.Commands/CommandService.cs

@@ -43,8 +43,12 @@ namespace Discord.Commands
             _typeReaders = new ConcurrentDictionary<Type, ConcurrentDictionary<Type, TypeReader>>();
 
             _defaultTypeReaders = new ConcurrentDictionary<Type, TypeReader>();
-            foreach (var type in PrimitiveParsers.SupportedTypes)
+            foreach (Type type in PrimitiveParsers.SupportedTypes)
+            {
                 _defaultTypeReaders[type] = PrimitiveTypeReader.Create(type);
+                if (type.GetTypeInfo().IsValueType)
+                    _defaultTypeReaders[typeof(Nullable<>).MakeGenericType(type)] = NullableTypeReader.Create(type);
+            }
 
             var entityTypeReaders = ImmutableList.CreateBuilder<Tuple<Type, Type>>();
             entityTypeReaders.Add(new Tuple<Type, Type>(typeof(IMessage), typeof(MessageTypeReader<>)));

src/Discord.Net.Commands/Readers/NullableTypeReader.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Threading.Tasks;
+
+namespace Discord.Commands
+{
+    internal static class NullableTypeReader
+    {
+        public static TypeReader Create(Type type)
+        {
+            type = typeof(NullableTypeReader<>).MakeGenericType(type);
+            return Activator.CreateInstance(type) as TypeReader;
+        }
+    }
+
+    internal class NullableTypeReader<T> : TypeReader
+        where T : struct
+    {
+        private readonly TryParseDelegate<T> _tryParse;
+
+        public NullableTypeReader()
+        {
+            _tryParse = PrimitiveParsers.Get<T>();
+        }
+
+        public override Task<TypeReaderResult> Read(ICommandContext context, string input)
+        {
+            T value;
+            if (_tryParse(input, out value))
+                return Task.FromResult(TypeReaderResult.FromSuccess(new Nullable<T>(value)));
+            return Task.FromResult(TypeReaderResult.FromSuccess(new Nullable<T>()));
+        }
+    }
+}