code: def get_db_prep_value(self, value, connection, prepared=False):
          
          if prepared:
              return value
  
          if value is None:
              return []
  
          values = value if self.multi_valued_field else [value]
          prepared_values = [self.get_prep_value(v) for v in values]
  
          # Remove duplicates.
          # https://tools.ietf.org/html/rfc4511#section-4.1.7 :
          # "The set of attribute values is unordered."
          # We keep those values sorted in natural order to avoid useless
          # updates to the LDAP server.
          return list(sorted(set(v for v in prepared_values if v)))
docs: Prepare a value for DB interaction.
  
          Returns:
          - list(bytes) if not prepared
          - list(str) if prepared