The following shall be void and of no effect:
(1) Any contract for personal separation between husband and wife;
(2) Every extra-judicial agreement, during marriage, for the dissolution of the conjugal partnership of gains or of the absolute community of property between husband and wife;
(3) Every collusion to obtain a decree of legal separation, or of annulment of marriage;
(4) Any simulated alienation of property with intent to deprive the compulsory heirs of their legitime.