code: def content_type(self):  # type: () -> str
          
          # todo(mvsusp): consider a better default content-type
          return self.headers.get('ContentType') or self.headers.get(
              'Content-Type') or _content_types.JSON
docs: The request's content-type.
  
          Returns:
              (str): The value, if any, of the header 'ContentType' (used by some AWS services) and 'Content-Type'.
                      Otherwise, returns 'application/json' as default.