Add Nullable ComponentTypeConverter and TypeReader (#2307)

* add nullable ComponentTypeConverter and TypeReader

* add converter and reader to interactionservice

src/Discord.Net.Interactions/InteractionService.cs

@@ -223,7 +223,8 @@ namespace Discord.Interactions
                 new ConcurrentDictionary<Type, Type>
                 {
                     [typeof(Array)] = typeof(DefaultArrayComponentConverter<>),
-                    [typeof(IConvertible)] = typeof(DefaultValueComponentConverter<>)
+                    [typeof(IConvertible)] = typeof(DefaultValueComponentConverter<>),
+                    [typeof(Nullable<>)] = typeof(NullableComponentConverter<>)
                 });
 
             _typeReaderMap = new TypeMap<TypeReader, string>(this, new ConcurrentDictionary<Type, TypeReader>(),
@@ -234,7 +235,8 @@ namespace Discord.Interactions
                     [typeof(IUser)] = typeof(DefaultUserReader<>),
                     [typeof(IMessage)] = typeof(DefaultMessageReader<>),
                     [typeof(IConvertible)] = typeof(DefaultValueReader<>),
-                    [typeof(Enum)] = typeof(EnumReader<>)
+                    [typeof(Enum)] = typeof(EnumReader<>),
+                    [typeof(Nullable<>)] = typeof(NullableReader<>)
                 });
         }
 

src/Discord.Net.Interactions/TypeConverters/ComponentInteractions/NullableComponentConverter.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Threading.Tasks;
+
+namespace Discord.Interactions
+{
+    internal class NullableComponentConverter<T> : ComponentTypeConverter<T>
+    {
+        private readonly ComponentTypeConverter _typeConverter;
+
+        public NullableComponentConverter(InteractionService interactionService, IServiceProvider services)
+        {
+            var type = Nullable.GetUnderlyingType(typeof(T));
+
+            if (type is null)
+                throw new ArgumentException($"No type {nameof(TypeConverter)} is defined for this {type.FullName}", "type");
+
+            _typeConverter = interactionService.GetComponentTypeConverter(type, services);
+        }
+
+        public override Task<TypeConverterResult> ReadAsync(IInteractionContext context, IComponentInteractionData option, IServiceProvider services)
+            => string.IsNullOrEmpty(option.Value) ? Task.FromResult(TypeConverterResult.FromSuccess(null)) : _typeConverter.ReadAsync(context, option, services);
+    }
+}

src/Discord.Net.Interactions/TypeReaders/NullableReader.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Threading.Tasks;
+
+namespace Discord.Interactions
+{
+    internal class NullableReader<T> : TypeReader<T>
+    {
+        private readonly TypeReader _typeReader;
+
+        public NullableReader(InteractionService interactionService, IServiceProvider services)
+        {
+            var type = Nullable.GetUnderlyingType(typeof(T));
+
+            if (type is null)
+                throw new ArgumentException($"No type {nameof(TypeConverter)} is defined for this {type.FullName}", "type");
+
+            _typeReader = interactionService.GetTypeReader(type, services);
+        }
+
+        public override Task<TypeConverterResult> ReadAsync(IInteractionContext context, string option, IServiceProvider services)
+            => string.IsNullOrEmpty(option) ? Task.FromResult(TypeConverterResult.FromSuccess(null)) : _typeReader.ReadAsync(context, option, services);
+    }
+}