That line didn’t have fileset() before. The fileset() code was only for the line that’s inside of the ant.'jacoco.instrument' block that was using fileset(). It doesn’t make sense as part of the conditional.
You have custom logic here (even if someone else wrote it) for a specific use case. You need to understand what that use case is so that you know which parts of the code are relevant to maintaining that behavior. If there are multiple classesDirs, and only some exist what do you expect to happen? That would determine how to modify the rest of your code.
