You’ll sometimes hear, “Absence of evidence is not evidence of absence.”
Absence of evidence is evidence of absence—of unicorns, for example. It’s just not proof of absence. On the other hand, millennia of absence of evidence is a strong argument for probability of absence, or non-existence if you prefer.
Someone suggested that the response to that is, “A claim that is put forward without evidence can be reliably dismissed unless and until evidence is provided.”