code: def _convert_list_tuples_to_dict(self, headers_list):
          # type: (List[Tuple[str, str]]) -> Dict[str, str]
          
          headers_dict = {}  # type: Dict
          if headers_list is not None:
              for header_tuple in headers_list:
                  key, value = header_tuple[0], header_tuple[1]
                  if key in headers_dict:
                      headers_dict[key] = "{}, {}".format(
                          headers_dict[key], value)
                  else:
                      headers_dict[header_tuple[0]] = value
          return headers_dict
docs: Convert list of tuples from headers of request object to
          dictionary format.
  
          :param headers_list: List of tuples made up of two element
              strings from `ApiClientRequest` headers variable
          :type headers_list: List[Tuple[str, str]]
          :return: Dictionary of headers in keys as strings and values
              as comma separated strings
          :rtype: Dict[str, str]