Function is_null_userdata

library/LuaTools.cpp:75–78

void dfhack_printerr(lua_State *S, const std::string &str);

inline bool is_null_userdata(lua_State *L, int idx)
{
    return lua_islightuserdata(L, idx) && !lua_touserdata(L, idx);
}

inline void AssertCoreSuspend(lua_State *state)
{