recursion when packed variadic template has zero elements

I have a class like this:

template<std::size_t T, std::size_t... Args>
class A{
   public:
      std::array<int,summation<Args...>::value> x;
}

where summation is defined as:

template<std::size_t size, std::size_t... sizes>
    struct summation
    {
        static const std::size_t value = size + summation<sizes...>::value;
    };


template<std::size_t size>
    struct summation<size>
    {
        static const std::size_t value = size;
    };

The problem is that when Args is empty (i.e., I only specify the T template) the base case does not work and I get a compilation error message:

error: wrong number of template arguments (0, should be 1 or more)

How can I modify the recursion of summation to also properly handle the case when sizeof...(Args)==0 and return a value of 0 for the summation in this case? I am using C++11. Thanks