When the office of President of the National Commission is vacant or a person occupying such office is, by reason of absence or otherwise, unable to perform the duties of his office, these shall be performed by the senior-most member of the National Commission:
     Provided that where a retired Judge of a High Court or a person who has been a Judicial Member is a member of the National Commission, such member or where the number of such members is more than one, the senior-most person amongst such members, shall preside over the National Commission in the absence of President of that Commission.