A: That depends on whether you have any defense. If you're not sure if you have any defense, consult an attorney. If you know for certain that you have no defense, contact plaintiff's counsel to make an offer (for example, 50% of the total, payable in installments of $50 a month), and see if you can amicably resolve it.
If not amicably resolved by the time of your pretrial conference, the judge will likely order you to mediate (possibly the same day), where you'd have to get into a discussion with a mediator to see if you the matter can be amicably resolved at that time. If you have no viable defense, and you don't amicably resolve it, you are likely looking at liability for a substantial amount of attorney's fees and costs, in addition to the amount being claimed right now.
A: You ask if it would be void "based on this law", without saying which law you are referring to. Did you leave something out, or did you mean to ask if there is any law that would void it out? I suggest you re-phrase.
A: Did you need to get medical treatment? If yes, keep the food frozen in order to analyzed by a lab and consult a personal injury attorney immediately. If no, though you have a potential claim for money damages, the minimal damage to you is such that it's likely that no attorney will be interested in representing you. If the latter is the case, you have the option of presenting a claim in writing to the restaurant, which would be turned over to their insurance company - which would view the damage as minimal and which might or might not make some very small offer, such as a few hundred bucks, to settle the matter.