I haven't read the meta-analysis you linked, but based on my prior reading of this topic, I'd suggest it's more correct to say "It probably has not been measure

I haven't read the meta-analysis you linked, but based on my prior reading of this topic, I'd suggest it's more correct to say "It probably has not been measured." Whereas it could still exist, but just elude attempts to measure. I also realize you can say this about anything, but ego depletion is one of those topics where it may seem very likely to be true based on our own experience as living humans, but where measuring its effect across a set of humans is incredibly challenging.