docs: def check_guest_exist(check_index=0):
      """Check guest exist in database.
  
      :param check_index: The parameter index of userid(s), default as 0
  
      """
  
      def outer(f):
          @six.wraps(f)
          def inner(self, *args, **kw):
              userids = args[check_index]
  
              if isinstance(userids, list):
                  # convert all userids to upper case
                  userids = [uid.upper() for uid in userids]
                  new_args = (args[:check_index] + (userids,) +
                              args[check_index + 1:])
              else:
                  # convert the userid to upper case
                  userids = userids.upper()
                  new_args = (args[:check_index] + (userids,) +
                              args[check_index + 1:])
                  userids = [userids]
  
              self._vmops.check_guests_exist_in_db(userids)
  
              return f(self, *new_args, **kw)
          return inner
      return outer