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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 _close_open_date_ranges(self, record):
 """If a date range is missing the start or end date, close it by copying the date from the existing value."""

        date_ranges = (('beginDate', 'endDate'),)
        for begin, end in date_ranges:
            if begin in record and end in record:
                return
            elif begin in record:
                record[end] = record[begin]
            elif end in record:
                record[begin] = record[end]