Method stack_reference

include/sol/stack_reference.hpp:137–137

	public:
		stack_reference() noexcept = default;
		stack_reference(lua_nil_t) noexcept : stack_reference() {};
		stack_reference(lua_State* L, lua_nil_t) noexcept : stateless_stack_reference(L, 0), luastate(L) {
		}