code: def update(self, password=values.unset):
          
          return self._proxy.update(password=password, )
docs: Update the CredentialInstance
  
          :param unicode password: The password will not be returned in the response
  
          :returns: Updated CredentialInstance
          :rtype: twilio.rest.api.v2010.account.sip.credential_list.credential.CredentialInstance