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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 hdf5(self):
 """Path of output hdf5 folder if relevant, None otherwise."""

        if self._rundir['hdf5'] is UNDETERMINED:
            h5_folder = self.path / self.par['ioin']['hdf5_output_folder']
            if (h5_folder / 'Data.xmf').is_file():
                self._rundir['hdf5'] = h5_folder
            else:
                self._rundir['hdf5'] = None
        return self._rundir['hdf5']