As I understand it, they aren't exactly lens artifacts, they're stars in the foreground. The telescope can't see past them and we don't know what's there. To me, it would defeat the observational mission of the JWST to fill it in with some pixels that were similar to the rest of the background. However, I also think you raise a good point, since all these images are constructed from non-visible infra-red light and many decisions are made in that conversion process.