In every Gen is it a Type combination that doesn´t have any weaknesses?

Question

I mean like Gen 4 Spiritomb (Dark/Ghost)
It can even be type that doesn´t exist.

Answer 1

No, out of all possible type combos, only the Ghost/Dark lacks weaknesses without the use of a Ability. So overall there have only been 5 Pokemon without a weakness:
Sableye
Spiritomb
Eelektross family
However, with the introduction of the Fairy type, Ghost/Dark gained a weakness, meaning no type combo can have no weakness without the use of a Ability.