Translation of "Caduc" in English

Exemple : "le testament est caduc si le légataire meurt avant le testateur"

Example: "the will is void if the legatee dies before the testator"

J'ai un secret, mais si je te le dis, il deviendrait caduc.

I have a secret, but if I were to tell you, it would be lost.

Et "un contrat valablement formé devient caduc si l'un de ses éléments essentiels disparaît"

and "a validly formed contract lapses if one of its essential elements disappears"