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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 _cron_id(cron):
    '''SAFETYBELT, Only set if we really have an identifier'''
    cid = None
    if cron['identifier']:
        cid = cron['identifier']
    else:
        cid = SALT_CRON_NO_IDENTIFIER
    if cid:
        return _ensure_string(cid)