c++ unique template

unique.h

template<typename T, T null_value, void (*release)(T)>
class unique {
public:
    // TODO: should we include an empty ctor?
    // unique() : m_val(null_value) { }
    unique() = delete;
    unique(T val) : m_val(val) { }
    unique(unique&& source) : m_val(source.m_val) {
        source.m_val = null_value;
    }
    ~unique() {
        if (m_val != null_value) {
            release(m_val);
        }
    }
    unique(const unique&) = delete;
    unique & operator=(const unique &) = delete;

    T val() const { return m_val; }
private:
    T m_val;
};
static inline void unique_close_fd(int fd) { close(fd); }
using unique_fd = unique<int, -1, unique_close_fd>;