DISCHARGE BY IMPOSSIBIL ITY OF PERFORMANCE. As a general rule a subsequent impossibility of performance will not ex cuse a party who has made an unconditional promise to do a thing. But a group of excepstions to the rule have been established by judicial precedents. Thus, if the impossibility arises from a change in the law of the country, the promisor will be exonerated. Or. if the continued existence of a specific thing is essential to the performance of the contract, its destruction, without fault of either party, discharges the contract. And if the object of the contract is the rendering of personal services, it will be discharged by impossi bility arising from the death or illness of the prom isor.