code: def combine_filters(filters, operator=AND):
      # type: (Iterable[Any], int) -> Optional[Union[LDAPFilter, LDAPCriteria]]
      
      if not filters:
          return None
  
      if not hasattr(filters, "__iter__") or is_string(filters):
          raise TypeError("Filters argument must be iterable")
  
      # Remove None filters and convert others
      ldap_filters = []
      for sub_filter in filters:
          if sub_filter is None:
              # Ignore None filters
              continue
  
          ldap_filter = get_ldap_filter(sub_filter)
          if ldap_filter is not None:
              # Valid filter
              ldap_filters.append(ldap_filter)
  
      if not ldap_filters:
          # Do nothing
          return None
      elif len(ldap_filters) == 1:
          # Only one filter, return it
          return ldap_filters[0]
  
      new_filter = LDAPFilter(operator)
      for sub_filter in ldap_filters:
          # Direct combination
          new_filter.append(sub_filter)
  
      return new_filter.normalize()
docs: Combines two LDAP filters, which can be strings or LDAPFilter objects
  
      :param filters: Filters to combine
      :param operator: The operator for combination
      :return: The combined filter, can be None if all filters are None
      :raise ValueError: Invalid filter string found
      :raise TypeError: Unknown filter type