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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 GetSectionByIndex(self, section_index):
 """Retrieves a specific section based on the index. Args: section_index (int):
 index of the section. Returns: VolumeExtent: a volume extent or None if not available. """

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

    if section_index < 0 or section_index >= len(self._sections):
      return None

    return self._sections[section_index]