code: def credentials_lists(self):
          
          if self._credentials_lists is None:
              self._credentials_lists = CredentialListList(self._version, trunk_sid=self._solution['sid'], )
          return self._credentials_lists
docs: Access the credentials_lists
  
          :returns: twilio.rest.trunking.v1.trunk.credential_list.CredentialListList
          :rtype: twilio.rest.trunking.v1.trunk.credential_list.CredentialListList