No seeds found

[jaime-iranzo]

Hi,

When running CasCollect without a user-defined seed, it dies prematurely with "no seeds collected, ending run".

I guess the reason could be a bug in line 385 of CasCalloect.py (if os.stat(seed).st_size == 0:), which should check "seeds" instead of "seed". As it is, if a user-defined seed has not been provided, it terminates execution as it had not found any seed.