Even North Korea has nukes, and a sworn enemy even, and no nuclear holocaust.
Everyone who knows something about nukes, know about "MAD", Mutually Assured Destruction, so, eh... it makes no difference if a country has nukes, they aren't gonna be more likely to use them offensively than anyone else - North Korea, the grand pariah of the world, being the best example.
With Israel most likely having nukes, MAD becomes even more relevant, since Israel is Iran's "sworn enemy", meaning, it is very unlikely Iran will be an offender with nukes, knowing full well that Israel has the capacity to retaliate thoroughly.