code: function listUsers() {
    db.getUsers(function(getErr, users) {
      if (getErr) {
        return out.error(`error occurred: ${getErr}`);
      }
  
      if (!users.length) {
        return out.error("no users found");
      }
  
      return out.pjson(users.map((user) => _.pick(user, "username")));
    });
  }
docs: List users