PROTIP: The argument "there is no god" is also a positive claim. Let me explain.
First let's start with the question - what does "there is no god" actually mean? Well, from a very superficial level it means where some higher being exists or not, all other attributes to this god notwithstanding. The phrase "there is no god or gods" could just as easily refer to a conception of gods such as those in Buddhism, who are more sublime and long-lived beings than humans, but still ultimately mortal and don't control any sort of force in the universe. HOWEVER, in our current, monotheistic, created-universe understanding of "gods", when the term is used it is almost always referring to an omnipotent creator god; the *source of all existence.*
So what does this mean then? Well, it means that the question of whether god exists or not is better represented as why is there even existence in the first place. Most reasoned arguments theists use for the existence of a god don't argue about the superficial attributes of this god - they argue that god can be concluded by looking at the mechanisms of nature (i.e. existence) and extrapolating a source of being from that. Hence, the very premise of both theists and atheists arguments about the existence god isn't about god at all - it's about the fact that stuff already exists.
Where am I going with this? Well, since we know now that both sides now have the same starting premise ("stuff exists"), then we can see that BOTH of their conclusions about this existence inherently has to be positive, since by cold, intellectual cognition alone, there's no reason for there to be existence in the first place. The conclusions from theists thus becomes "there is existence, because God made it" (positive claim) and the conclusion from atheists thus becomes "there is existence, but it came about by random chance" (positive claim.)