Hangle nulls and vectors

Author: Pawel Wojciechowski

include/graphqlservice/GraphQLService.h

@@ -421,6 +421,11 @@ class [[nodiscard]] AwaitableScalar
 	std::variant<T, std::future<T>, std::shared_ptr<const response::Value>> _value;
 };
 
+template <typename T>
+struct is_vector : std::false_type {};
+
+template <typename T>
+struct is_vector<std::vector<T>> : std::true_type {};
 // Field accessors may return either a result of T, an awaitable of T, or a std::future<T>, so at
 // runtime the implementer may choose to return by value or defer/parallelize expensive operations
 // by returning an async future or an awaitable coroutine.
@@ -436,11 +441,24 @@ class [[nodiscard]] AwaitableObject
 	}
 
 	template <typename U>
-	AwaitableObject(U&& value,std::enable_if_t<!std::is_assignable_v<T,U>>* = nullptr)
-	: _value ( std::make_shared<typename T::element_type>(value) )
+	AwaitableObject(U&& value,std::enable_if_t<!std::is_assignable_v<T,U> && !is_vector<U>::value  >* = nullptr)
+	: _value ( value?std::make_shared<typename T::element_type>(value): std::shared_ptr<typename T::element_type>())
 	{
 	}
 
+	template <typename U>
+	AwaitableObject(U&& value,std::enable_if_t<!std::is_assignable_v<T,U> && is_vector<U>::value  >* = nullptr)
+	{
+		T vec;
+		for(auto v:value){
+			if(v)
+				vec.push_back(std::make_shared<typename T::value_type::element_type>(v));
+			else
+				vec.push_back(std::shared_ptr<typename T::value_type::element_type>());
+		}
+		_value=std::move(vec);
+	}
+
 	struct promise_type
 	{
 		[[nodiscard]] AwaitableObject<T> get_return_object() noexcept