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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 GetRootKey(self):
 """Retrieves the root key. Returns: WinRegistryKey: Windows Registry root key or None if not available. """

    regf_key = self._regf_file.get_root_key()
    if not regf_key:
      return None

    return REGFWinRegistryKey(regf_key, key_path=self._key_path_prefix)