In court? By calling a credible witness, perhaps an expert, who says “X isn’t occurring.”

Yea but you can’t prove it’s not occurring. All you can show is lack of evidence that it is occurring.

Absence of evidence is not evidence of absence, but evidence of absence does exist. “Claiming that it is impossible to prove a negative is a pseudologic, because there are many proofs that substantiate negative claims”: https://en.wikipedia.org/wiki/Evidence_of_absence