Node-SQLite3 result undefined outside of loop

I use this code get all entries from the "users" table in a sqlite3 library in nodejs. When I check the value rows inside the function it is defined, but the calling function only gets an undefined object.

exports.getUsers = function() {
  exports.getDb().serialize(function() {
    exports.getDb().all('SELECT * FROM users', function(err, rows) {
      if(err !== null) {
        winston.error(err);
      }
      return rows !== undefined ? rows : [];
    });
  });
};