code: def get_sentry(self, username):
          
          filepath = self._get_sentry_path(username)
  
          if filepath and os.path.isfile(filepath):
              try:
                  with open(filepath, 'rb') as f:
                      return f.read()
              except IOError as e:
                  self._LOG.error("get_sentry: %s" % str(e))
  
          return None
docs: Returns contents of sentry file for the given username
  
          .. note::
              returns ``None`` if :attr:`credential_location` is not set, or file is not found/inaccessible
  
          :param username: username
          :type username: :class:`str`
          :return: sentry file contents, or ``None``
          :rtype: :class:`bytes`, :class:`None`