Weird contract

gistfile1.txt

  #include <eosiolib/eosio.hpp>
  #include <eosiolib/print.hpp>

  using namespace eosio;

  class addressbook : public eosio::contract {

  public:
    using contract::contract;

    addressbook(account_name self): contract(self) {}

    [[eosio::action]]
    void upsert(account_name user, std::string first_name, std::string last_name, std::string street, std::string city, std::string state) {
      require_auth( user );
      address_index addresses(_self, user );
      auto iterator = addresses.find(user);
      if( iterator == addresses.end() )
      {
        addresses.emplace(user, [&]( auto& row ) {
         row.key = user;
         row.first_name = first_name;
         row.last_name = last_name;
         row.street = street;
         row.city = city;
         row.state = state;
        });
        INLINE_ACTION_SENDER( addressbook, notify )( N(addressbook), { user, N(active) }, { user, std::string("You added your address to addressbook") } );
      }
      else {
        addresses.modify(iterator, user, [&]( auto& row ) {
          row.key = user;
          row.first_name = first_name;
          row.last_name = last_name;
          row.street = street;
          row.city = city;
          row.state = state;
        });
        INLINE_ACTION_SENDER( addressbook, notify )( N(addressbook), { user, N(active)}, { user, std::string("You updated your address.") } );
      }
    }

    [[eosio::action]]
    void notify(account_name user, std::string msg) {
      require_recipient(user);
    }

    [[eosio::action]]
    void remove(account_name user){
      require_auth( user );

      address_index addresses(_self, user);

      auto iterator = addresses.find(user);
      eosio_assert(iterator != addresses.end(), "Record does not exist");

      addresses.erase( iterator );
      eosio_assert(iterator == addresses.end(), "Address not erased properly");

      INLINE_ACTION_SENDER( addressbook, notify )( N(addressbook), { user, N(active)}, { user, std::string("You have successfully removed your record from addressbook") } );
    }

  private:
    struct [[eosio::table]] person {
      uint64_t key;
      std::string first_name;
      std::string last_name;
      std::string street;
      std::string city;
      std::string state;

      uint64_t primary_key() const { return key; }
      EOSLIB_SERIALIZE( person, (key)(first_name)(last_name)(street)(city)(state) )
    };

    typedef eosio::multi_index<N(person), person> address_index;

  };

  EOSIO_ABI( addressbook, (upsert) )