Removing all cards in your hand and your side of the field from play is a cost to activate “Card of Sanctity”. If you have no other cards except for “Card of Sanctity”, you cannot activate it. You must have at least 1 other card on your side of the field or in your hand.
You can chain “Null and Void” to “Card of Sanctity”.
“Card of Sanctity” itself is NOT removed from play by its cost.