docs: def _get_mime_type(self, buff):
          """Get the MIME type for a given stream of bytes
  
          :param buff: Stream of bytes
          :type buff: bytes
  
          :rtype: str
  
          """
          if self._magic is not None:
              return self._magic.id_buffer(buff)
          else:
              try:
                  return mimetypes.guess_type("f." + imghdr.what(0, buff))[0]
              except (IOError, TypeError):
                  logging.warning("Couldn't detect content type of avatar image"
                                  ". Specify the 'contentType' parameter explicitly.")
                  return None