docs: def expire_by_email(self, email_address, **kwargs):
          """Expires tokens for an email address or email addresses.
  
          :param email_address: the string email address or emails addresses to
              expire tokens for.
          :param reason: the codified reason for the tokens.  If explicitly set
              to None, this will expire all tokens for the email provided.
          """
          if not email_address:
              # no email(s) provided.  Nothing to do.
              return None
  
          if isinstance(email_address, (set, list, tuple)):
              email_address = [e.strip() for e in set(email_address)
                               if e and e.strip()]
  
              # make sure there's at least 1 valid email address
              if len(email_address) <= 0:
                  # no valid emails
                  return None
  
              kwargs['email_address__in'] = email_address
          else:
              kwargs['email_address'] = email_address
  
          # try setting the reason default if one exists (in the case of proxy
          # models)
          if 'reason' not in kwargs and self.model.reason_default:
              kwargs['reason'] = self.model.reason_default
  
          if 'reason' in kwargs and kwargs.get('reason') is None:
              # explicitly setting the reason to None will expire all tokens for
              # a user regardless of the reason.
              del kwargs['reason']
  
          self.filter(**kwargs).update(expires=datetime(1970, 1, 1))