def _create_payload(self, symbols):
payload = {'<STR_LIT>': self.access_key}<EOL>if symbols is not None:<EOL><INDENT>payload['<STR_LIT>'] = '<STR_LIT:U+002C>'.join(symbols)<EOL><DEDENT>return payload<EOL>
Creates a payload with no none values.

        :param symbols: currency symbols to request specific exchange rates.
        :type symbols: list or tuple
        :return: a payload.
        :rtype: dict