Who Can File Declaration of Nullity of Marriage?

It is axiomatic that the validity of marriage and the unity of the family are enshrined in our Constitution and statutory laws, hence any doubts attending the same are to be resolved in favor of the continuance and validity of the marriage and that the burden of proving the nullity of the same rests at all times upon the petitioner. (Singson vs. Singson, G.R. No. 210766, Jan. 08, 2018)

Who has the burden of proving the nullity? Is this a Void marriage? See the Complete Decision: Singson vs. Singson, G.R. No. 210766, Jan. 08, 2018. This is another case of Psychological Incapacity.