[Spades] bidding defaults

For the judge scripts... in the xs0 judge script, during bidding, if the script outputs something invalid or nothing on the willyoudoublenil call, the judge script randomly picks nil, doublenil, or 1-13. If the script outputs something invalid or nothing after responding "no" to the willyoudoublenil call, the judge script randomly picks nil, or 1-13.

Is this what all judge scripts should do?

Yup, for any response that is not valid, a random valid response should be used.

Besides things that have been discussed about the judge scripts, will potential misunderstandings like this count as bugs and disqualify judge scripts, whose authors may not have known?

Depends on actual cases. But generally, if something was discussed and resolved in these forums, the scripts should do as was said. That's what the forums are for...

If something was not discussed, it's best to ask, but if not, the script should do something reasonable. For example, in the above case (if this thread didn't happen), it's reasonable not to use doublenil, but is not reasonable to always play 13...