Split the Arrays inside a JSON object with as many rows as there are objects

@Vladyslav, I agree, this appears to be a bug. The $input0.count value type doesn’t appear to be comparable type to 0. I suggest you open a ticket to support.

In the meantime, I think I found this expression to work for your case:
$input0.count.toString() == "0" ? "File Not Found" : "File exists"

Another hack is to place a JSON Formatter + JSON Parser between the Gate and Mapper. That seems to correct the expected type.