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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 GetVolumeByIndex(self, volume_index):
 """Retrieves a specific volume based on the index. Args: volume_index (int):
 index of the volume. Returns: Volume: a volume or None if not available. """

    if not self._is_parsed:
      self._Parse()
      self._is_parsed = True

    if volume_index < 0 or volume_index >= len(self._volume_identifiers):
      return None

    volume_identifier = self._volume_identifiers[volume_index]
    return self._volumes[volume_identifier]