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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 api_registration_check(self):
        '''
            Reach out to the inventory API to check
            whether a machine exists.

            Returns
                True    system exists in inventory
                False   system does not exist in inventory
                None    error connection or parsing response
        '''
        if self.config.legacy_upload:
            return self._legacy_api_registration_check()

        logger.debug('Checking registration status...')
        results = self._fetch_system_by_machine_id()
        if not results:
            return results

        logger.debug('System found.')
        logger.debug('Machine ID: %s', results[0]['insights_id'])
        logger.debug('Inventory ID: %s', results[0]['id'])
        return True