Warlock can use Enchantment Transfusion, too, remember.
If the Wizard is really dedicated to having Nullify on at all times, the Warlock can instead curse his or her own Demon, and then Enchantment Transfusion those curses over to the Wizard. Doing this won't trigger the Wizard's Nullify.
And if the Warlock is clever, one of the enchantments Transfused onto the Wizard will be a Nullify cast by the Warlock, to counter the Purge Magic / Purify that the Wizard will have prepared.
And then if the Wizard is clever, they'll have Destroy Magic available instead.
And then if the Warlock is clever.... You can see how this goes.