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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _convert_list_tuples_to_dict(self, headers_list):
 # type: (List[Tuple[str, str]]) -> Dict[str, str] """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] """

        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