Marriage may be annulled for the following causes:
1. Where the marriage between the parties is prohibited by law.
2. Where either party was impotent at the time of marriage.
3. Where either party had a husband or wife living at the time of the marriage, provided they have not, with a knowledge of such fact, lived and cohabited together after the death or marriage dissolution of the former spouse of such party.
4. Where either party was a ward under a guardianship and was found by the court to lack the capacity to contract a valid marriage.