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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 CopyToDateTimeString(self):
 """Copies the APFS timestamp to a date and time string. Returns: str: date and time value formatted as: "YYYY-MM-DD hh:mm:ss.#########" or None if the timestamp is missing or invalid. """

    if (self._timestamp is None or self._timestamp < self._INT64_MIN or
        self._timestamp > self._INT64_MAX):
      return None

    return super(APFSTime, self)._CopyToDateTimeString()