Thanks for the snippet! And thank you for NOT telling me how to fix it, I love sleepless nights ;-)
After this night I read Vautrin's reply (after, very clever :-/) and tried this

...
foreach (0..$#good_ones) {
    if (defined $good_ones[$_]) {
        print ...
...
[download]

The error messages are gone. Is this the solution? Maybe I'm silly, but I still have no idea why the code produced an error massage at all.