Article 237 of Personal Status Law

If the bequest to those mentioned in the preceding article is of usufruct alone, and none of them exists at the testator's death, it shall belong to the testator's heirs. If an entitled person exists at the testator's death or thereafter, the usufruct shall belong to that person and to every entitled person who comes into existence after him until they have all died out, whereupon the usufruct shall belong to the testator's heirs. When there is no prospect of other legatees coming into existence, the corpus shall be returned to the testator's heirs.