How can the payer for the modified table = 0?

Question

statstable.modify( st, 0, [&]( auto& s ) {
   s.supply += quantity;
});

Here is some code from the eosio.token contract. How can the payer be 0? what does it mean?

Here are the params for the modify function btw (as per developers.eos.io):

modify(itr, payer, updater) where:

• itr - an iterator pointing to the object to be updated

• payer - account name of the payer for the Storage usage of the updated row

• updater - lambda function that updates the target object

Answer 1

This line indicates that passing 0 in the payer argument keeps the existing payer for the entry.

https://github.com/EOSIO/eos/blob/v1.0.8/libraries/chain/apply_context.cpp#L456