How do you know its non-existent if you don't research?

Well, you can't know that, even if you do research. To know if something does not exist, you would first have to have a complete knowledge of everything that does exist. I'm not aware of any omniscient people, are you?

I could search for evidence of the case we're talking about for the rest of my life and never find any. It doesn't mean it doesn't exist, just that I was never able to find it.

This is why it's the responsibility of the person making the claim that something does exist (like this case) to provide evidence to support their claim.

I reject your premise . Nice try though.

It's not my premise. It's a basic foundation of logical thought and has been around for thousands of years.

Feel free to call up your favorite search engine and look up "proving a negative logical fallacy" or "burden of proof (philosophy)".

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Edited to add; I am curious as to what you would accept as proof that this case we're talking about never happened. Could you give me an example of what you have in mind?